An error slipped into the current program. I’m just quoting what the boss said in his letter:
It’s kind of, meow, difficult.
First, he checks one and says that you can start.
And then he starts to check either this or that, and says that you should wait.
And I see two messages: first saying that you can, and then right away saying that you cannot. And I do not know what to do.
Let him just say when you can start, and when you cannot.
It’s a pity that you had to deal with the tasks “analyzing boss requirements” and “fixing bugs using mind-reading” so early. But nothing can be done about it. Let’s figure out what the error is and what the boss wants.
We can see from the letter that under certain conditions the program logs two messages at once. For the error to be detected, it must first be reproduced. So let’s change the values of the input data.
<!DOCTYPE html><html lang="en" class="no-js"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width,initial-scale=1"><script>var b=document.documentElement.classList;b.remove('no-js');if(!window.Promise||!window.sessionStorage||!!sessionStorage.getItem('muller.v2')){b.add('muller')}</script><link rel="dns-prefetch" href="https://assets.htmlacademy.org"><script async src="https://www.googletagmanager.com/gtag/js?id=G-MXPCRXM48C"></script><script>
window.dataLayer = window.dataLayer || [];
function gtag(){dataLayer.push(arguments);}
gtag('js', new Date());
gtag('config', 'G-MXPCRXM48C');
</script><script type="text/javascript">
(function(e,t){var n=e.amplitude||{_q:[],_iq:{}};var r=t.createElement("script")
;r.type="text/javascript"
;r.integrity="sha384-d/yhnowERvm+7eCU79T/bYjOiMmq4F11ElWYLmt0ktvYEVgqLDazh4+gW9CKMpYW"
;r.crossOrigin="anonymous";r.async=true
;r.src="https://cdn.amplitude.com/libs/amplitude-5.2.2-min.gz.js"
;r.onload=function(){if(!e.amplitude.runQueuedFunctions){
console.log("[Amplitude] Error: could not load SDK")}}
;var i=t.getElementsByTagName("script")[0];i.parentNode.insertBefore(r,i)
;function s(e,t){e.prototype[t]=function(){
this._q.push([t].concat(Array.prototype.slice.call(arguments,0)));return this}}
var o=function(){this._q=[];return this}
;var a=["add","append","clearAll","prepend","set","setOnce","unset"]
;for(var u=0;u<a.length;u++){s(o,a[u])}n.Identify=o;var c=function(){this._q=[]
;return this}
;var l=["setProductId","setQuantity","setPrice","setRevenueType","setEventProperties"]
;for(var p=0;p<l.length;p++){s(c,l[p])}n.Revenue=c
;var d=["init","logEvent","logRevenue","setUserId","setUserProperties","setOptOut","setVersionName","setDomain","setDeviceId","setGlobalUserProperties","identify","clearUserProperties","setGroup","logRevenueV2","regenerateDeviceId","groupIdentify","onInit","logEventWithTimestamp","logEventWithGroups","setSessionId","resetSessionId"]
;function v(e){function t(t){e[t]=function(){
e._q.push([t].concat(Array.prototype.slice.call(arguments,0)))}}
for(var n=0;n<d.length;n++){t(d[n])}}v(n);n.getInstance=function(e){
e=(!e||e.length===0?"$default_instance":e).toLowerCase()
;if(!n._iq.hasOwnProperty(e)){n._iq[e]={_q:[]};v(n._iq[e])}return n._iq[e]}
;e.amplitude=n})(window,document);
amplitude.getInstance().init("df11525b6880a3c5e2af14f9b6238408", null,{
includeUtm: true,
includeGclid: true,
includeReferrer: true,
deviceIdFromUrlParam: true
}, function (instance) {
window.amplitudeLoaded = true;
});
</script><link rel="stylesheet" href="https://assets.htmlacademy.org/css/core.v284.css"><link rel="stylesheet" href="https://assets.htmlacademy.org/css/profile.v236.css"><link rel="stylesheet" href="https://assets.htmlacademy.org/css/course.v246.css"><link rel="stylesheet" href="https://assets.htmlacademy.org/css/course-interface-light.v20.css"><link rel="stylesheet" href="https://assets.htmlacademy.org/css/course-interface-en.v2.css"><script src="https://assets.htmlacademy.org/js/sentry.js" data-sentry="3774884cc81746ed84c0ba7c5cd4ac7b" data-project="26" data-version="2"></script><link rel="stylesheet" href="/css/custom.css"><link rel="stylesheet" href="/css/cookies.css"><link rel="preload" as="script" href="https://assets.htmlacademy.org/js/general.v274.js"><title>Logic traps — Conditions — HTML Academy</title><meta name="csrf-token" content="6064caf322823086fca37a7326b9bd2a54"><meta property="og:type" content="website"><meta property="og:site_name" content="HTML Academy"><meta name="twitter:url" property="og:url" content="https://htmlacademy.org"><meta name="twitter:title" property="og:title" content="Interactive online courses HTML Academy"><meta name="twitter:description" property="og:description" content="Together we’ll learn how to work with real code, solve true-to-life problems, use cutting edge technologies. Minimum of boring theory and lots of practical tasks."><meta name="twitter:image" property="og:image" content="https://htmlacademy.org/og/htmlacademy.png"><meta name="twitter:card" content="summary_large_image"><link rel="canonical" href="https://htmlacademy.org/courses/javascript-programming/conditions/negation"><meta name="theme-color" content="#2f358f"></head><body class="course-interface course-interface--light" data-base="/assets/courses/3/"><header class="page-header page-header--course"><div class="page-header__inner"><div class="page-header__top"><a class="page-header__logo" href="/" aria-label="HTML Academy Home"><img src="https://assets.htmlacademy.org/img/logo--small.svg?cs=1218aec0be4a5f23db79ad29a14e30f7f9fb9a25" width="24" height="36" alt="HTML Academy"></a><nav class="main-nav main-nav--mini" role="navigation"><div class="main-nav__course-nav"><a class="main-nav__course-item main-nav__course-button main-nav__course-button--prev" href="/courses/javascript-programming/conditions/and-or">Logical operators: &&, ||</a><div class="main-nav__course-item main-nav__course-list main-nav__course-list--collapsed"><b class="main-nav__course-title">Conditions</b><span class="main-nav__course-stat">13/17</span><div class="main-nav__course-contents"><a class="main-nav__course-contents-link" href="/courses/javascript-programming/conditions">Back to the list of tasks</a><ul class="main-nav__course-contents-list"><li class="main-nav__course-contents-item"><a href="/courses/javascript-programming/conditions/simple-if">1. Simple fork</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-programming/conditions/if-else">2. Let’s use an alternative</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-programming/conditions/simple-compare">3. Simple comparisons</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-programming/conditions/or-equal">4. Comparisons permitting equality</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-programming/conditions/equality">5. Equality, inequality</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-programming/conditions/string-compare">6. Strict string comparison</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-programming/conditions/numeric-compare">7. Strict number comparison</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-programming/conditions/then-action">8. Condition-based actions</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-programming/conditions/else-action">9. If the condition is not fulfilled</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-programming/conditions/value-condition">10. Values as a condition</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-programming/conditions/nested-if">11. Nested conditions</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-programming/conditions/and-or">12. Logical operators: &&, ||</a></li><li class="main-nav__course-contents-item main-nav__course-contents-item--current"><a href="/courses/javascript-programming/conditions/negation">13. Logic traps</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-programming/conditions/nesting-deeper">14. Logical negation</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-programming/conditions/logic-operators">15. Let’s combine logical operators</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-programming/conditions/summary">16. Summary of “Conditions”</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-programming/conditions/walk-calculator">17. Second program: “How long to take a walk for?”</a></li></ul></div></div><a class="main-nav__course-item main-nav__course-button main-nav__course-button--next" href="/courses/javascript-programming/conditions/nesting-deeper">Logical negation</a></div><ul class="main-nav__list main-nav__list--user main-nav__list--user-guest"><li class="main-nav__item" itemprop="name"><a class="main-nav__link" href="/signup?redirect_url=%2Fcourses%2Fjavascript-programming%2Fconditions%2Fnegation" title="Sign up" data-modal="open" data-value="register" itemprop="url"><span class="main-nav__icon" aria-hidden="true"><svg aria-hidden="true"><use xlink:href="/img/sprites/general.svg#user"></use></svg></span>Sign up</a></li><li class="main-nav__item main-nav__item--login" itemprop="name"><a class="main-nav__link" href="/login?redirect_url=%2Fcourses%2Fjavascript-programming%2Fconditions%2Fnegation" title="Log in" data-modal="open" data-value="login" itemprop="url"><span class="main-nav__icon" aria-hidden="true"><svg aria-hidden="true"><use xlink:href="/img/sprites/general.svg#login"></use></svg></span>Log in</a></li></ul></nav></div></div></header><div class="notice notice--error js--initialization-error hidden"><a class="notice__link" href="#"><span class="notice__title js--initialization-error__content"></span></a><button class="notice__close" type="button">Close</button></div><main class="course-container course-interface__content task"><div class="course-container__inner"><article class="course-layout js--user-settings" data-theme="ace/theme/ha-light-default" data-taskid="60" data-storageKey="task-60"><div class="course-loading-overlay course-layout__loading-overlay hidden"><div class="course-loading-overlay__inner"><span class="course-loading-overlay__image"><svg width="70" height="70" viewBox="0 0 70 70" xmlns="http://www.w3.org/2000/svg"><defs><clipPath id="clip-path" transform="translate(-3.2 -3.22)"><circle cx="38.65" cy="38.78" r="34.15" fill="#d5dcf1" stroke-dasharray="0"/></clipPath></defs><style>.keks-loader-circle { stroke-dasharray: 500; stroke-dashoffset: 1000; animation: dash 1.5s linear reverse infinite; } @keyframes dash { 0% { stroke-dashoffset: 0; }, 25% { stroke-dashoffset: 1000; }, 50% { stroke-dashoffset: 0; }, 75% { stroke-dashoffset: 1000; }, 100% { stroke-dashoffset: 0; } }</style><circle cx="35" cy="33" r="33" transform="matrix(.01053 -.96378 .9652 .01054 2.506 68.344)" fill="#D5DCF1" stroke="#F15A29" stroke-width="3.5"/><g transform="matrix(.9237 -.01338 0 .98374 2.38 -2.91)" clip-path="url(#clip-path)"><path d="M55.25 62.93c-1-2.23-2.81-5-4-7.27-.87-1.58-.39-3.35-2.32-3.16 0 0-2.81.84-3.88 1-1.07.16-4.65 3-5.91 3.44-1.55.56-3.29.19-4.93.19-1.686-.555-3.333-1.223-4.93-2-1-.74-7.26-2.32-7.45-1.77-.19.55-6.03 13.66-5.58 14.23.29.28 15 8.57 15.78 8.75 1.113.666 2.188 1.394 3.22 2.18.48.56 12.47-6 12.47-6.93 0 0 7.944-4.177 8.52-4.38 2.1-.74 2.804-.31-1-4.28h.01z" fill="#CF4A27"/><path d="M41.56 55.18c-.57-.47-1.06.46-.29 1 3.19 2.37 5.86 5.87 6.17 9.84-1.69-.58-3.44-.73-5.11-1.37a.53.53 0 0 0-.77.56 16.56 16.56 0 0 1-.07 4.57 12 12 0 0 1-4.29-2.88c-.29-.36-.87 0-.87.38-.17 1.7-.06 3.25-.9 4.72l-.15.15-.17-.17c-.82-1.46-.71-3-.88-4.68 0-.38-.59-.74-.87-.38a12.11 12.11 0 0 1-4.29 2.86 16.56 16.56 0 0 1-.07-4.56.53.53 0 0 0-.77-.56c-1.67.64-3.42.8-5.11 1.37.31-4 3-7.48 6.17-9.84.77-.56.29-1.49-.29-1-3.77 2.7-6.68 6.8-6.77 11.46a.51.51 0 0 0 .77.46c1.55-.71 3.33-.82 5-1.35-.15 1.61.13 3.14.13 4.79a.54.54 0 0 0 .77.46 21.65 21.65 0 0 0 4.47-2.6 9.28 9.28 0 0 0 1.09 4.37 2.32 2.32 0 0 0 .43.62l.1.06h.07a.59.59 0 0 0 .61-.1 2.1 2.1 0 0 0 .47-.72 9.49 9.49 0 0 0 1-4.31 22.19 22.19 0 0 0 4.48 2.6.54.54 0 0 0 .77-.46c0-1.65.28-3.17.13-4.79 1.68.53 3.45.64 5 1.35a.51.51 0 0 0 .77-.46c-.11-4.67-3-8.77-6.79-11.47z" fill="#F1662A"/><path d="M35.49 62.47s5-.38 6-1.49c4.65-5.4 9.1-6.7 9.1-6.7l-.68-1.39-14.53 2.8-13.37-2.7v1.49s3.49 1.21 8.24 6.61c1 1.1 5.14 1.38 5.24 1.38" style="isolation:isolate" fill="#A23922" opacity=".5"/><path d="M22.12 52.88c-1.75 5.5-5.33 8.66-6 14.34" fill="#F1662A"/><path d="M21.54 52.78c-1.64 5-5.33 9.12-6 14.43-.09.65.64 2 1.07 0 .68-5.21 4.45-9.31 6-14.16.19-.64-.87-.91-1.07-.27zm28.08.55c2 4.57 5.13 8.57 6.4 13.4.2.65 1.4.35 1.31-.29-1.25-4.93-4.7-9-6.83-13.67-.2-.55-1.17-.08-.88.57z" fill="#151841"/></g><circle class="keks-loader-circle" cx="35" cy="33" r="33" transform="matrix(.01053 -.96378 .9652 .01054 2.506 68.344)" fill="#D5DCF1" stroke-width="3.5" fill-opacity="0" stroke="#2A2F5A"/><path d="M54.838 32.26c-.084 4.648-.716 9.52-3.152 13.594-1.08 1.86-1.525 3.2-3.246 4.5-1.44 1.042-4.65.428-7.03 2.334 0 0-3.245 2.79-6.034 2.604-2.79-.186-5.403-2.427-5.403-2.427-1.348-1.293-4.584-1.562-6.574-2.25-2.344-.865-6.036-8.053-6.296-9.3l-.633-2.426c-.808-1.86-.994-3.98-1.98-5.887-.673-1.056-1.178-2.21-1.496-3.422-.55-2.603-1.163-5.28-1.628-7.875-.81-3.896-2.427-10.23.186-13.502 0 0 2.94-.67 8.192 4.845 2.52 2.25 5.04 6.51 8.193 7.7.62-.678 1.18-1.41 1.673-2.186.86.79 1.986 1.22 3.153 1.21.716 0 1.264-.69 1.794-.69.46.105.912.248 1.35.428 1.858.78 1.793-.864 2.872-.78 1.078.083 1.078 2.073 3.42.78l1.163-.018c2.976-3.115 8.908-11.084 13.948-9.96 4.502 1.126-.808 18.533-2.342 22.773" fill="#F15A29"/><path d="M59.422 11.486c-.93-3.72-5.216-2.334-7.56-.782-2.037 1.452-3.884 3.155-5.495 5.068-.716.78-1.442 1.646-2.25 2.51l-.93 1.042c-.312 0-.624.027-.93.084-.633.084-1.08.605-1.71.353-.35-.208-.664-.472-.93-.78-.554-.41-1.308-.41-1.86 0-.304.488-.882.73-1.442.605-.527-.242-1.07-.444-1.627-.605-.484-.003-.956.147-1.35.428-1.077.688-2.52-.26-3.328-.865-.246-.2-.608-.162-.81.084-.395.632-.84 1.232-1.328 1.795-2.427-1.21-4.138-3.47-5.766-5.45-1.53-1.704-3.177-3.3-4.928-4.78-.823-.765-1.765-1.394-2.79-1.86-.862-.325-1.788-.446-2.706-.352-.81 0-1.162 1.21-1.44 1.86-.434 1.19-.648 2.45-.633 3.72.097 2.626.46 5.237 1.077 7.792.363 1.562.55 3.198.93 4.76.243 1.77.667 3.507 1.265 5.19.812 1.57 1.532 3.19 2.157 4.844.362 1.21.808 2.427 1.078 3.636.312 1.247.735 2.464 1.265 3.635 1.11 2.42 2.566 4.667 4.323 6.668 1.71 1.86 4.585 1.47 6.75 2.51 2.075 1.47 4.325 2.94 6.845 3.292 2.52.353 5.04-1.562 7.208-3.2 1.71-.78 3.608-.78 5.402-1.384 1.795-.605 2.79-2.604 3.608-4.073 1.27-2.134 2.238-4.434 2.874-6.835.503-2.078.79-4.204.855-6.34.05-.433.125-.86.223-1.285 1.22-3.304 2.213-6.687 2.976-10.126.827-3.72 1.813-7.71 1.004-11.158zm-.93 4.584c-.225 2.128-.586 4.24-1.078 6.323-.71 3.194-1.602 6.345-2.67 9.438-.262.617-.407 1.276-.427 1.945-.092 1.935-.34 3.86-.744 5.756-.58 2.34-1.49 4.585-2.706 6.668-.93 1.646-1.794 3.636-3.868 4.156-.93.26-1.796.354-2.614.52.007-.335-.352-.553-.647-.392-.022.012-.042.025-.06.04-.91.582-1.78 1.22-2.614 1.906-1.71 1.21-3.607 2.334-5.672 2.25-1.535-.203-2.994-.792-4.24-1.71-.363-.177-1.44-1.042-1.627-1.126-.716-.52-1.35-.93-2.074-1.47-.363-.26-.716.085-.716.522-.716-.177-1.348-.26-1.98-.428-1.86-.428-2.874-1.86-3.962-3.376-1.68-2.457-2.94-5.18-3.72-8.052-.27-.93-.632-1.86-.93-2.94-.31-1.408-.862-2.754-1.626-3.98-.773-1.45-1.29-3.022-1.526-4.648-.363-1.562-.716-3.2-.995-4.845-.448-2.426-.996-4.76-1.266-7.27-.186-2.158-.186-4.585 1.08-6.51.57-.054 1.146-.026 1.71.083.9.318 1.727.818 2.427 1.47 1.265.93 2.344 2.073 3.506 3.115 2.706 2.334 5.496 7.44 8.555 7.97.693-.605 1.297-1.303 1.796-2.075.79.56 1.707.908 2.668 1.014.508.065 1.022-.06 1.442-.354.54-.408 1.295-.373 1.794.084.67.408 1.52.375 2.158-.084.25-.282.57-.49.93-.604.344.18.657.412.93.688.59.452 1.366.584 2.073.353.447-.083.633-.26 1.08-.353.32.042.646-.02.93-.177 1.525-1.646 2.975-3.375 4.5-4.937 1.676-1.96 3.766-3.527 6.12-4.585 1.44-.604 3.328-.78 3.96.865.428 1.55.486 3.177.167 4.752z" fill="#151841"/><path d="M48.524 33.04c-.236-.845-.932-1.483-1.795-1.646-.705-.074-1.413-.102-2.12-.083.083-.604.548-2.51-.81-2.333-.716 0-1.44 2.073-1.86 2.603-.715 1.042-1.162.78-1.264-.428-.102-1.208.446-2.854-.55-3.115-.715-.083-1.263 1.293-1.524 2.158-.083.427-.548.78-.362-2.25 0-.782 0-2.855-.447-2.94h-.186c-1.264.085-2.157 4.94-2.52 6.324-.27-1.386-1.71-7.273-2.79-5.98-.14.61-.202 1.234-.185 1.86 0 .427-.084 3.375-.447 2.854-.186-.864-1.162-2.603-1.71-2.334-.995.865-.187 2.074-.447 3.292s-.632 1.47-1.264.354c-.363-.52-.995-2.604-1.71-2.688-1.266-.176-.93 1.73-.93 2.334-.69-.076-1.383-.104-2.075-.083-.852.156-1.558.75-1.86 1.56-.084.177 0 6.668 5.95 6.76.862.043 1.72-.103 2.52-.427.52-.13.995-.558 1.45-.214l6.11.4c.342-.36.847-.51 1.33-.4.925.493 1.934.808 2.976.93 3.06 0 5.765-1.21 6.667-3.98.307-.103-.056-2.353-.15-2.53z" fill="#EFA75B"/><path d="M23.67 33.998s3.783-.354 4.77.177c1.095.612 1.896 1.642 2.22 2.854-.492.19-1.003.333-1.524.427-.616.09-1.237.15-1.86.177-3.06-.354-3.607-3.636-3.607-3.636zm23.6.51s-3.72-.52-4.772-.082c-1.16.554-2.038 1.564-2.426 2.79l1.44.52c.604.18 1.23.266 1.86.26 3.18-.195 3.897-3.487 3.897-3.487zm-7.03 2.605c.27.084 1.16.428 1.44.52.53.155 1.076.242 1.627.26h.186c2.706-.083 3.608-2.854 3.72-3.29-1.053-.157-2.116-.235-3.18-.233-.487-.017-.973.042-1.442.176-1.128.46-1.992 1.402-2.35 2.567z" fill="#FFF"/><path d="M32.223 43.26c-.152-1.397-.03-2.81.363-4.157 0 0 .93-2.94 2.343-3.2 3.72-.687 4.054 7.44 4.054 7.44-4.334 1.906-6.76-.084-6.76-.084z" fill="#F47741"/><path d="M45.204 44.292c-.508-.698-1.296-1.14-2.157-1.21-1.71-.176-7.56 1.126-7.56 1.126v.065c-.772-.205-5.98-1.6-7.56-1.45-.875.04-1.692.45-2.25 1.125-.446.864.084 2 .55 2.938.74 1.35 1.788 2.505 3.058 3.375.48.332 1.045.513 1.627.522 4.492.084 4.77-2.585 4.77-2.464l.075-.465c.186 0-.363 2.79 4.054 2.79.542.102 1.1.073 1.628-.084 1.305-.853 2.39-2 3.17-3.35.41-.92 1.043-1.96.596-2.918z" fill="#EFA75B"/><path d="M31.963 50.968c-.197-.004-.358-.157-.372-.353-.018-.207.158-.378.364-.354 3.245-.26 3.505-2.156 3.608-2.25-.006-.19.183-.325.362-.26.193.01.35.16.363.354 0 .084 0 1.906 3.422 2 .192.008.348.16.362.353-.018.19-.172.34-.363.353-1.352.11-2.68-.4-3.61-1.386-.095-.096-.16-.22-.185-.353-.982 1.174-2.423 1.866-3.952 1.898z" fill="#151841"/><path d="M32.14 43.427c.186-.52 3.608.083 3.608.083s2.975-.688 3.422.084c-.05.288-.175.557-.363.78-.515-.056-1.037.004-1.525.178-.333.61-.488 1.304-.446 2-.222.394-.574.7-.995.864-.398-.112-.75-.354-.994-.688.047-.75-.146-1.496-.55-2.13-.27-.26-1.264.084-1.626-.083l-.53-1.088zm6.89.242c-.05.286-.175.556-.363.78-.503-.063-1.015-.012-1.497.148-.333.612-.487 1.305-.446 2-.222.394-.574.7-.995.864-.4-.112-.75-.354-.996-.688.053-.76-.14-1.515-.55-2.157-.268-.26-1.263.084-1.626-.084-.26-.23-.45-.53-.55-.864" fill="#CF4A27"/><path d="M35.748 47.853c-.587-.226-1.072-.655-1.367-1.21-.022-.634-.144-1.262-.362-1.86h-.567c-.31.073-.636.043-.93-.082-.35-.253-.61-.616-.734-1.03-.082-.17.006-.374.186-.43.172-.083.38 0 .447.177.056.278.215.524.445.69h.586c.37-.086.757-.023 1.08.175.413.585.634 1.284.632 2v.353c.185.177.4.32.632.428.22-.18.42-.382.595-.605-.004-.29.024-.58.083-.865.026-.48.22-.94.55-1.292.506-.235 1.07-.325 1.626-.26.077-.108.14-.227.185-.353-.038-.148.042-.3.186-.353.145-.11.352-.07.447.083.084.084.27.428-.446 1.21-.083.083-.185.176-.27.083-.422-.033-.848-.004-1.264.084-.215.502-.323 1.043-.316 1.59v.176c-.326.57-.824 1.023-1.422 1.293zm-7.198-14.04c-.788-.226-1.61-.314-2.427-.26-1.264 0-2.436.082-2.52.082h-.38v.354s.715 3.55 3.96 3.895c.693.006 1.385-.025 2.074-.093.27-.084 1.71-.428 1.71-.428-.025-1.56-.975-2.956-2.417-3.552zm.53 3.207c-.558.142-1.135.2-1.71.177-1.14-.075-2.16-.728-2.707-1.73-.247-.37-.432-.78-.548-1.21.455 0 1.18-.092 2.073-.175h.596c-.084.688-.242 2.464.483 2.334.725-.13.837-1.46.93-2.13h.112c.937.492 1.647 1.33 1.98 2.334-.388.176-.793.31-1.21.4zm18.365-2.864c-1.104-.145-2.215-.232-3.33-.26-.546-.01-1.093.05-1.626.176-1.166.483-2.08 1.425-2.53 2.604l-.158.79 1.795.623c.558.153 1.132.24 1.71.26h.28c3.245-.177 4.137-3.72 4.137-3.72l.084-.353zm-1.264 1.86c-.54 1.394-2.882 1.646-2.966 1.646-.517-.02-1.03-.11-1.525-.26-.186-.085-.633-.26-1.08-.43.374-.966 1.117-1.746 2.065-2.165 0 .68.158 1.953.81 2.083.65.13.613-1.535.566-2.26.934.005 1.865.064 2.79.177-.11.316-.473.65-.66 1.17z" fill="#151841"/><path d="M19.26 39.27c.535 1.362 1.56 2.473 2.874 3.115.534.312 1.204-.07 1.207-.69.002-.285-.15-.55-.397-.695-.918-.46-1.65-1.222-2.073-2.158-.344-.957-1.972-.52-1.61.428zm29.45 3.125c1.083-.59 2.01-1.428 2.706-2.446.3-.556-.112-1.228-.743-1.21-.293.007-.56.17-.698.428-.568.776-1.306 1.412-2.158 1.86-.394.23-.517.742-.27 1.125.263.376.773.482 1.163.242z" fill="#EFA75B" stroke-width="13"/><path d="M16.025 32.436c1.525-1.386 2.427-4.408 2.79-6.835-.084.354 2.613.43 4.138-1.208 1.078-1.125.446-2-.186-3.375-1.71-3.552-4.585-6.323-7.384-8.918-.716-.69-1.44-2.428-2.706-2-.995.353-.93 3.2-.716 4.073 1.09 7.448 4.065 18.263 4.065 18.263zm37.372-.78c-1.704-1.826-2.822-4.12-3.208-6.585 0 .354-2.614.354-4.056-1.29-.995-1.127-.362-1.86.363-3.117 1.86-3.198 4.863-5.718 7.746-8.136.81-.604 1.627-1.47 2.79-.93.994.428.715 2.334.548 3.115-1.083 5.72-2.48 11.376-4.183 16.943z" fill="#FFF"/><path d="M53.564 20.422c-1.98.51-4.138 1.636-5.105 3.487-.43-2.196 1.645-4.65 3.393-5.832.333-.21.312-.703-.037-.886-.162-.085-.357-.076-.512.022-2.157 1.562-4.417 4.5-3.784 7.188.076.262.354.41.614.325l-.075.28c-.085.603.93.864.994.26.446-2.158 2.706-3.376 4.77-3.897.372-.076.522-.526.27-.81-.133-.15-.342-.204-.53-.138zM17.457 18.06c-.55-.354-.995.428-.55.865 1.433 1.004 3.182 3.05 3.395 4.956-.93-1.86-3.05-2.975-5.105-3.486-.386-.005-.633.41-.445.747.042.076.103.14.176.184 2.073.52 4.324 1.73 4.77 3.896.106.328.5.46.78.26.273.192.653.06.745-.26.735-2.66-1.6-5.728-3.766-7.16z" fill="#F1662A"/></svg></span><p class="course-loading-overlay__message"><b class="course-loading-overlay__message-title">Loading…</b><br><span class="course-loading-overlay__message-text">Everything will be ready in few seconds</span></p></div></div><div class="course-layout__sidebar course-theory"><div class="course-theory__inner course-theory__inner--left-stub"><button class="course-theory__close icon-close icon-close--light" type="button">Close</button><ul class="course-tabs course-tabs--non-interactive course-layout__theory-heading js--theory-tabs"><li class="course-tabs__item course-tabs__item--external course-tab course-tab--centered"><span class="course-tab__icon"><svg aria-hidden="true"><use xlink:href="/img/sprites/courses.svg#icon-theory"></use></svg></span><span class="course-tab__title">Theory</span></li><li class="course-tabs__item course-tabs__item--internal course-tab course-tab--centered course-tab--active js--theory-tab__theory"><span class="course-tab__icon"><svg aria-hidden="true"><use xlink:href="/img/sprites/courses.svg#icon-theory"></use></svg></span><span class="course-tab__title">Theory</span></li><li class="course-tabs__item course-tabs__item--internal course-tab course-tab--centered js--theory-tab__comments"><span class="course-tab__icon"><svg aria-hidden="true" style="width: 16px; height: 16px; fill: #2e2c9c;"><use xlink:href="/img/sprites/up.svg#comment"></use></svg></span><span class="course-tab__title">Comments</span></li></ul><section class="course-theory__content"><div class="js--theory-pane__theory course-theory__content-inner"><h1 class="course-theory__content-heading">Logic traps</h1><div class="course-theory__content-text"><p>An error slipped into the current program. I’m just quoting what the boss said in his letter:</p><blockquote><p>It’s kind of, meow, difficult.</p><p>First, he checks one and says that you can start.</p><p>And then he starts to check either this or that, and says that you should wait.</p><p>And I see two messages: first saying that you can, and then right away saying that you cannot. And I do not know what to do.</p><p>Let him just say when you can start, and when you cannot.</p></blockquote><p>It’s a pity that you had to deal with the tasks “analyzing boss requirements” and “fixing bugs using mind-reading” so early. But nothing can be done about it. Let’s figure out what the error is and what the boss wants.</p><p>We can see from the letter that under certain conditions the program logs two messages at once. For the error to be detected, it must first be reproduced. So let’s change the values of the input data.</p></div></div><div class="js--theory-pane__comments hidden course-theory__content-inner"><div class="course-theory__content-text"><h2 class="course-theory__content-heading">Comments</h2><div id="disqus_thread"></div><script>
/**
* RECOMMENDED CONFIGURATION VARIABLES: EDIT AND UNCOMMENT THE SECTION BELOW TO INSERT DYNAMIC VALUES FROM YOUR PLATFORM OR CMS.
* LEARN WHY DEFINING THESE VARIABLES IS IMPORTANT: https://disqus.com/admin/universalcode/#configuration-variables */
var disqus_config = function () {
this.page.url = "https://htmlacademy.org/courses/javascript-programming/conditions/negation";
this.page.identifier = "task-60";
};
(function() { // DON'T EDIT BELOW THIS LINE
var d = document, s = d.createElement('script');
s.src = 'https://htmlacademy.disqus.com/embed.js';
s.setAttribute('data-timestamp', +new Date());
(d.head || d.body).appendChild(s);
})();
</script><noscript>Please enable JavaScript to view the <a href="https://disqus.com/?ref_noscript">comments powered by Disqus.</a></noscript></div></div></section><div class="course-theory__controls"><button class="button button--close" type="button">To the task</button></div></div></div><div class="course-layout__column course-layout__column--left"><ul class="js--course-tabs course-tabs course-layout__course-tabs"><li class="course-tabs__item course-tab js--editor-tab course-tabs__item--limited course-tabs__item--limited-large course-tab--active" data-editor="js"><span class="course-tab__title course-tab__title--indent"><span class="course-tab__title-part course-tab__title-part--active">script.js</span></span></li></ul><div class="course-layout__editors"><div class="js--editor course-editor course-layout__editor" id="" data-tab="js" data-split=""><span class="course-editor__label"><span class="course-editor__label-item">JavaScript</span></span><div class="course-editor__item" id="js-editor">var enoughDevelopers = false;
var techAvailable = false;
var onVacation = false;
var onSickLeave = false;
if (enoughDevelopers && techAvailable) {
console.log('You can start the project');
}
if (onVacation || onSickLeave) {
console.log('It is better to wait');
}
</div></div></div><div class="course-editor-controls"><button class="course-editor-controls__item course-editor-controls__item--answer" type="button">Show the answer</button></div><div class="js--feedback course-unhappy"><button class="js--feedback-btn course-unhappy__button" type="button"><span class="sr-only">Complain</span><svg aria-hidden="true"><use xlink:href="/img/sprites/courses.svg#unhappy"></use></svg></button><div class="js--feedback-modal course-unhappy__modal course-unhappy__modal--step-one"><form method="POST" action="/courses/javascript-programming/conditions/negation/signal" class="course-unhappy__form form"><input type="hidden" name="csrf_name" value="csrf69aea82a831ea"><input type="hidden" name="csrf_value" value="1cd4cb814a2871b626b496b06a6bff11"><p class="course-unhappy__text">What didn’t you like in this task?</p><div class="course-unhappy__slide"><div class="course-unhappy__wrap"><div class="course-unhappy__list"><label class="checkbox checkbox--small"><input class="checkbox__input" name="problems" value="1" type="checkbox"><span class="checkbox__text">The code check doesn’t work</span></label><label class="checkbox checkbox--small"><input class="checkbox__input" name="problems" value="2" type="checkbox"><span class="checkbox__text">The task is too difficult</span></label><label class="checkbox checkbox--small"><input class="checkbox__input" name="problems" value="3" type="checkbox"><span class="checkbox__text">The theory is hard to understand</span></label><label class="checkbox checkbox--small"><input class="js--feedback-other-checkbox checkbox__input" name="problems" value="0" type="checkbox"><span class="checkbox__text">Other (will write below)</span></label></div><div class="course-unhappy__message"><label class="sr-only" for="id-message">Другое (сейчас напишу)</label><textarea class="field field--area" id="id-message" name="message" placeholder="For example, a typo in the word «heading»"></textarea></div></div></div><button class="course-unhappy__control course-unhappy__control--prev" type="button"><span class="sr-only">Prev</span><svg aria-hidden="true"><use xlink:href="/img/sprites/landings.svg#arrow"></use></svg></button><button class="course-unhappy__control course-unhappy__control--next" type="button" disabled><span class="sr-only">Next</span><svg aria-hidden="true"><use xlink:href="/img/sprites/landings.svg#arrow"></use></svg></button><button class="js--submit-btn button" disabled>Submit</button></form><p class="course-unhappy__result hidden">Thanks! We’ll fix everything at once!</p></div></div></div><div class="course-layout__column course-layout__column--right"><span class="course-separator-control"><svg aria-hidden="true"><use xlink:href="/img/sprites/courses.svg#icon-arrows-separator"></use></svg></span><div class="course-browser"><div class="course-browser__menu"><span class="course-browser__menu-item course-browser__address"><span class="course-browser__menu-item-inner">Console</span></span><button class="js--autorun course-browser__menu-item course-browser__menu-button course-browser__menu-button--text-with-icon course-browser__menu-button--autorun course-browser__menu-button--autorun-on" title="Autorun" type="button"><span class="course-browser__menu-item-inner"><svg aria-hidden="true"><use xlink:href="/img/sprites/courses.svg#icon-autorun"></use></svg>
Autorun
</span></button><button class="course-browser__menu-item course-browser__menu-button course-browser__menu-button--expand" type="button"><svg xmlns="http://www.w3.org/2000/svg" width="11" height="11" viewBox="0 0 11 11"><path d="M1.375 5.125v4.5h4.5m3.75-3.75v-4.5h-4.5" fill="none" fill-rule="evenodd" stroke="currentColor"></path></svg></button></div><div class="course-browser__notification js--browser-change-heading hidden"><p class="course-browser__notification-text">The code has changed, click “Run” or turn autorun on.</p><button class="course-browser__notification-button course-browser__notification-button--play js--close" type="button"><svg aria-hidden="true"><use xlink:href="/img/sprites/courses.svg#icon-play"></use></svg>
Run</button></div><div class="course-browser__content"><div class="console js--console"><h2 class="sr-only">Result</h2><div class="console__content js--console__content"></div></div></div><div class="course-goals js--goals"><div class="course-goals__heading"><span class="course-goals__heading-title"><span class="course-goals__count-label">Goals</span><span class="course-goals__count">completed</span></span><button class="course-goals__button course-goals__button--expand js--goals__expand" type="button"><svg aria-hidden="true"><use xlink:href="/img/sprites/courses.svg#icon-collapse"></use></svg></button><a class="course-goals__button course-goals__button--next button button--green button--without-border hidden" href="/courses/javascript-programming/conditions/nesting-deeper" title="Logical negation"><svg aria-hidden="true"><use xlink:href="/img/sprites/courses.svg#arrow-white--mini"></use></svg></a></div><div class="course-goals__content"><p>In turn, change the values of the variables.</p><ol class="course-goals__list"><li class="course-goals__list-item">Indicate that there are enough developers.</li><li class="course-goals__list-item">Indicate that the developers mastered the technology.</li><li class="course-goals__list-item">Indicate that one of the developers is on vacation.</li></ol></div></div></div></div></article></div><div class="course-interface__overlay course-interface__overlay--active"></div></main><script
src="https://assets.htmlacademy.org/scripts/courses-spa/htmlacademy-task.v43.js"
data-task-type="js"
data-assets-path="https://assets.htmlacademy.org/scripts/courses-spa/"
data-lang="en"
></script><script>HtmlacademyTask.setRoutes({task:'/courses/javascript-programming/conditions/negation',check:'/courses/javascript-programming/conditions/negation/check'});</script><script>HtmlacademyTask.setup(function(){this.setView(JsView),this.setRunner(JsRunner),this.setChecker(JsChecker,function(){this.setMatcher(function(e){e.goal("change.developers").code('"#builtin.anything"; "#change.var"; "#builtin.anything"').assign("change.var","change.var.developers").goal("change.tech").takes("change.developers").assign("change.var","change.var.tech").goal("change.vacation").takes("change.developers").assign("change.var","change.var.vacation").fragment("change.var.developers").code("var enoughDevelopers = true").fragment("change.var.tech").code("var techAvailable = true").fragment("change.var.vacation").code("var onVacation = true")}),this.addGoal("1",function(e){return e.matches("change.developers")}),this.addGoal("2",function(e){return e.matches("change.tech")}),this.addGoal("3",function(e){return e.matches("change.vacation")})}),this.setAnswers([{goal:1,editor:"js",data:function(){this.tooltip("There are enough developers").at(0).find("false").replace("true")}},{goal:2,editor:"js",data:function(){this.tooltip("Developers mastered the technology").at(1).find("false").replace("true")}},{goal:3,editor:"js",data:function(){this.tooltip("One of the developers is on vacation").at(2).find("false").replace("true")}}])});</script><footer class="page-footer page-footer--tiny"><div class="page-footer__inner"><p><a href="/docs/cookies">Cookies</a> ∙
<a href="/docs/privacy">Privacy</a> ∙
<a href="/docs/agreement">License Agreement</a> ∙
<a href="/docs/about">About</a> ∙
<a href="/contacts">Contacts</a> ∙
© HTML Academy OÜ, 2019−2026
</p><div class="page-footer__financial"><img src="https://assets.htmlacademy.org/img/visa-white.svg?cs=96e54ec8c587db9d4b1d8d328ffd87c2ebfd9555" alt="VISA" title="VISA" width="35" height="35"><img src="https://assets.htmlacademy.org/img/mastercard-horizontal.v2.svg" alt="Mastercard" title="Mastercard" width="35" height="35"></div></div></footer><div class="modal"><div class="modal__inner"><div class="modal__wrapper js-login hidden"><button class="modal__close icon-close" type="button" title="Close" data-modal="close"></button><h4 class="modal__header">Log in</h4><ul class="modal__social"><li class="modal__social-link modal__social-link--fb"><a href="/login/fb?redirect_url=%2Fcourses%2Fjavascript-programming%2Fconditions%2Fnegation" rel="nofollow" title="Log in via Facebook"><svg aria-hidden="true"><use xlink:href="/img/sprites/general.svg#facebook"></use></svg></a></li><li class="modal__social-link modal__social-link--google"><a href="/login/google?redirect_url=%2Fcourses%2Fjavascript-programming%2Fconditions%2Fnegation" rel="nofollow" title="Log in via Google"><svg height="30" width="30" viewBox="0 0 512 512" xmlns="http://www.w3.org/2000/svg"><path fill="#ffffff" d="M457.732 216.625c2.628 14.041 4.063 28.743 4.063 44.098C461.796 380.688 381.481 466 260.204 466c-116.023 0-210-93.977-210-210s93.977-210 210-210c56.704 0 104.077 20.867 140.44 54.73l-59.204 59.197v-.135c-22.046-21.002-50-31.762-81.236-31.762-69.297 0-125.604 58.537-125.604 127.841 0 69.29 56.306 127.968 125.604 127.968 62.87 0 105.653-35.965 114.46-85.312h-114.46v-81.902h197.528z"/></svg></a></li></ul><div class="modal__or"><span>or</span></div><form class="modal__form form" action="/login?redirect_url=%2Fcourses%2Fjavascript-programming%2Fconditions%2Fnegation" autocomplete="off" method="post" data-submit="o"><input type="hidden" name="csrf_name" value="csrf69aea82a831ea"><input type="hidden" name="csrf_value" value="1cd4cb814a2871b626b496b06a6bff11"><div class="form__group"><label class="sr-only" for="login-email">Email</label><input class="field field--text field--full-width" type="email" name="email" placeholder="Email" value="" id="login-email"></div><div class="form__group"><label class="sr-only" for="login-password">Password</label><input class="field field--text field--full-width ym-disable-keys" type="password" name="password" placeholder="Password" id="login-password"></div><input class="button button--full-width" type="submit" data-submit-text="Logging in…" value="Log in"></form><p class="modal__forgot-password"><a href="/recover" data-modal="open" data-value="recover">Forgot your password?</a></p><a class="modal__bottom-link" href="/signup" data-modal="open" data-value="register">Sign up</a></div><div class="modal__wrapper js-register hidden"><button class="modal__close icon-close" type="button" title="Close" data-modal="close"></button><h4 class="modal__header">Sign up</h4><ul class="modal__social"><li class="modal__social-link modal__social-link--fb"><a href="/login/fb?redirect_url=%2Fcourses%2Fjavascript-programming%2Fconditions%2Fnegation" rel="nofollow" title="Log in via Facebook"><svg aria-hidden="true"><use xlink:href="/img/sprites/general.svg#facebook"></use></svg></a></li><li class="modal__social-link modal__social-link--google"><a href="/login/google?redirect_url=%2Fcourses%2Fjavascript-programming%2Fconditions%2Fnegation" rel="nofollow" title="Log in via Google"><svg height="30" width="30" viewBox="0 0 512 512" xmlns="http://www.w3.org/2000/svg"><path fill="#ffffff" d="M457.732 216.625c2.628 14.041 4.063 28.743 4.063 44.098C461.796 380.688 381.481 466 260.204 466c-116.023 0-210-93.977-210-210s93.977-210 210-210c56.704 0 104.077 20.867 140.44 54.73l-59.204 59.197v-.135c-22.046-21.002-50-31.762-81.236-31.762-69.297 0-125.604 58.537-125.604 127.841 0 69.29 56.306 127.968 125.604 127.968 62.87 0 105.653-35.965 114.46-85.312h-114.46v-81.902h197.528z"/></svg></a></li></ul><div class="modal__or"><span>or</span></div><form class="modal__form form" action="/signup?redirect_url=%2Fcourses%2Fjavascript-programming%2Fconditions%2Fnegation" autocomplete="off" method="post"><input type="hidden" name="csrf_name" value="csrf69aea82a831ea"><input type="hidden" name="csrf_value" value="1cd4cb814a2871b626b496b06a6bff11"><div class="form__group"><label class="sr-only" for="email">
Email
<span class="required"><span class="sr-only">Required field</span><span class="required__star">*</span></span></label><div class="form__group-fields"><input class="field field--text field--full-width" type="email" name="email" value="" id="email" required placeholder="Email"></div></div><div class="form__group"><label class="sr-only" for="password">
Password
<span class="required"><span class="sr-only">Required field</span><span class="required__star">*</span></span></label><div class="form__group-fields"><input class="field field--text field--full-width" type="password" name="password" value="" id="password" required placeholder="Password"></div></div><div class="form__group"><label class="checkbox"><input class="checkbox__input" type="checkbox" name="agreement" value="1" required><span class="checkbox__text"><span>By signing up, you agree to our <a href="/docs/agreement" target="_blank">License Agreement</a> and <a href="/docs/privacy" target="_blank">Privacy Policy</a>.</span></span></label></div><input class="button button--full-width" type="submit" data-submit-text="Signing up…" value="Sign up"></form><a class="modal__bottom-link" href="/login?redirect_url=%2Fcourses%2Fjavascript-programming%2Fconditions%2Fnegation" data-modal="open" data-value="login">Log in</a></div><div class="modal__wrapper modal__wrapper--no-btn-bottom js-recover hidden"><button class="modal__close icon-close" type="button" title="Close" data-modal="close"></button><h4 class="modal__header">Restore access</h4><p class="modal__text-accent">Have you forgotten your password or lost access to your profile? Enter your email connected to your profile and we will send you a link to restore access.</p><form class="modal__form form" action="/recover" autocomplete="off" method="post" data-submit="o"><input type="hidden" name="csrf_name" value="csrf69aea82a831ea"><input type="hidden" name="csrf_value" value="1cd4cb814a2871b626b496b06a6bff11"><div class="form__group"><label class="sr-only" for="recovery-email">Email</label><input class="field field--text field--full-width" type="email" name="email" placeholder="Email" value="" id="recovery-email"></div><script src='https://www.google.com/recaptcha/api.js'></script><div class="form__group"><div class="g-recaptcha" data-sitekey="6LetCTEqAAAAANROWtPzfC7Rfg9iIRiRt2k2FPn7"></div></div><input class="button button--full-width" type="submit" data-submit-text="Sending…" value="Send"></form><p class="modal__text">Forgot to connect your email to the profile? Email us and we’ll help.</p></div></div></div><script async src="https://assets.htmlacademy.org/js/general.v274.js" data-assets="https://assets.htmlacademy.org" data-require="toggle,navigation-courses,modal,form,nav"></script></body></html>