title: EcmaScript-6 backward compatibility
body: <p>I am curious to understand/figure-out if the ECMAScript-6 new-changes will work on the old browsers or not.</p>
  
  <p><strong>Why I am asking this question is:</strong></p>
  
  <p>I remember the introduction of <code>'use strict';</code> in ECMAScript-5, it was meant for the compatibility with the old versions. </p>
  
  <p>That means the old browsers will keep working fine and they will just ignore it when they encounter the <code>'use strict';</code> statement while parsing the new JavaScript code.</p>
  
  <p>And the new JS-engines will treat the statement <code>'use strict';</code> in some special way as detailed here <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Strict_mode" rel="noreferrer">Strict mode</a>.</p>
  
  <hr>
  
  <p>So, coming to the question</p>
  
  <p>I seriously doubt and curious to know how would the ECMAScript-5 compliant browsers behave when they will parse the ECMAScript-6 code.</p>
  
  <p>The reason for my doubt is ECMAScript-6 new features involve syntax change/updates. And the old browsers which are <em>new-syntax-unaware-engines</em> will start throwing errors when they encounter any of the new syntax from the following </p>
  
  <p><code>yield[*], Map, Set, WeakMap, function* foo(){}, =&gt;, for...of etc.</code></p>
  
  <p>My concern is has the decision/inclusion of new features in ECMAScript-6 taken care of supporting the old-browsers without any break of code? </p>
  
  <p><strong>If Yes</strong> then how?</p>
  
  <p><strong>If Not</strong> then what should I do to keep my <em>old-browser-users</em> happy? </p>
  
  <p>I see one solution to keep the users using old browsers happy by including some <a href="http://en.wikipedia.org/wiki/Source-to-source_compiler" rel="noreferrer">transpiler</a> like <a href="https://github.com/google/traceur-compiler" rel="noreferrer">traceur-compiler</a> in my project. This will convert my ECMAScript-6 code to ECMAScript-5 equivalent. But do I have any other solution to keep my <em>old-browser-users</em> happy?</p>