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POreturn opposite Boolean value in one line
 

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    <p>Common Javascript knowledge (or any programming language really) tells us that using <code>!variable</code> will equal the opposite value when it's Boolean (or converted to Boolean in a conditional, etc).</p> <h2>I have this Javascript:</h2> <pre><code>$(document).ready(function () { var addEvent = function (element, myEvent, fnc) { return ((element.attachEvent) ? element.attachEvent('on' + myEvent, fnc) : element.addEventListener(myEvent, fnc, false)); }; var openBar = false; addEvent(document.getElementById('toggle'), 'click', function (event) { var toggler = event.currentTarget, barWrap = document.getElementById('left-wrap'), newSize = (!openBar) ? 20 : 0; $(barWrap).animate({ width: (newSize / 100 * window.innerWidth) }, { queue: false, duration: 300, step: function (now) { toggler.style.right = now + 'px'; //barWrap.outerWidth = now; document.body.style.marginRight = now + 'px'; }, complete: function () { newSize = (newSize === 20) ? '20%' : '0%'; document.body.style.marginRight = newSize; toggler.style.right = newSize; barWrap.style.width = newSize; } }); return !openBar; }); }); </code></pre> <p>...that I threw into <a href="http://jsfiddle.net/3R5qe/" rel="nofollow">this JSFiddle</a>...which will show it open the toggle bar but not close it...with a lot of fluffy HTML and CSS too prettify it for y'all.</p> <p>Now, why on earth does the 3rd to last line NOT return the opposite value as it should? I have successfully used the following:</p> <pre><code>return openBar = !openBar; </code></pre> <p>but for some reason browsers and JSfiddle and JShint like to get mad when I do because they expect a conditional or value instead of assignment. But they don't fail to load. I also know I can use:</p> <pre><code>openBar = !openBar; return openBar; </code></pre> <p>or even</p> <pre><code>openBar = !openBar; return; </code></pre> <p>but I like to minimize everywhere I can and really just want to understand why this fundamentally is failing to work for me so I can correct it in the future.</p> <p>Is this in anyway incompatible with another browser (using Chrome 30 and Firefox 25) or possibly going to error out somewhere I'm not anticipating? </p> <p>Or is it more of an inconvenience/warning that I can ignore (like those things telling me to use === instead of == when comparing 0 when I know the result can only be a number)?</p>
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    1. CO`openbar` is not being modified when you do `return !openbar`. Behavior makes sense.
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    2. COEven though it's awkward - it's still syntactically correct: http://jsfiddle.net/JHTct/ and **does** work
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    3. COWhen I use !(openBar) in a separate part of the code it will alter the value correctly without using an assignment
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