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POJavaScript closure inside loops – simple practical example
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  1. POJavaScript closure inside loops – simple practical example
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    copied!<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false"> <div class="snippet-code"> <pre class="snippet-code-js lang-js prettyprint-override"><code>var funcs = []; for (var i = 0; i &lt; 3; i++) { // let's create 3 functions funcs[i] = function() { // and store them in funcs console.log("My value: " + i); // each should log its value. }; } for (var j = 0; j &lt; 3; j++) { funcs[j](); // and now let's run each one to see }</code></pre> </div> </div> </p> <p>It outputs this:</p> <blockquote> <p>My value: 3<br> My value: 3<br> My value: 3</p> </blockquote> <p>Whereas I'd like it to output:</p> <blockquote> <p>My value: 0<br> My value: 1<br> My value: 2</p> </blockquote> <hr> <p>The same problem occurs when the delay in running the function is caused by using event listeners:</p> <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false"> <div class="snippet-code"> <pre class="snippet-code-js lang-js prettyprint-override"><code>var buttons = document.getElementsByTagName("button"); for (var i = 0; i &lt; buttons.length; i++) { // let's create 3 functions buttons[i].addEventListener("click", function() { // as event listeners console.log("My value: " + i); // each should log its value. }); }</code></pre> <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;button&gt;0&lt;/button&gt;&lt;br&gt; &lt;button&gt;1&lt;/button&gt;&lt;br&gt; &lt;button&gt;2&lt;/button&gt;</code></pre> </div> </div> </p> <p>… or asynchronous code, e.g. using Promises:</p> <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false"> <div class="snippet-code"> <pre class="snippet-code-js lang-js prettyprint-override"><code>// Some async wait function const wait = (ms) =&gt; new Promise((resolve, reject) =&gt; setTimeout(resolve, ms)); for(var i = 0; i &lt; 3; i++){ wait(i * 100).then(() =&gt; console.log(i)); // Log `i` as soon as each promise resolves. }</code></pre> </div> </div> </p> <p>What’s the solution to this basic problem?</p>
 

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