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    <p>For the sake of completeness, I got to thinking about which method I should use to do this. There are basically two ways to do this as suggested by the other answers on this page.</p> <p><strong>Note:</strong> In general, extending the built-in prototypes in JavaScript is generally not recommended. I am providing as extensions on the String prototype simply for purposes of illustration, showing different implementations of a hypothetical standard method on the <code>String</code> built-in prototype.</p> <hr> <h3>Regular Expression Based Implementation</h3> <pre><code>String.prototype.replaceAll = function(search, replacement) { var target = this; return target.replace(new RegExp(search, 'g'), replacement); }; </code></pre> <h3>Split and Join (Functional) Implementation</h3> <pre><code>String.prototype.replaceAll = function(search, replacement) { var target = this; return target.split(search).join(replacement); }; </code></pre> <hr> <p>Not knowing too much about how regular expressions work behind the scenes in terms of efficiency, I tended to lean toward the split and join implementation in the past without thinking about performance. When I did wonder which was more efficient, and by what margin, I used it as an excuse to find out.</p> <p>On my Chrome Windows&nbsp;8 machine, <strong>the regular expression based implementation is the fastest</strong>, with the <strong>split and join implementation being 53% slower</strong>. Meaning the regular expressions are twice as fast for the lorem ipsum input I used.</p> <p>Check out this <a href="http://jsben.ch/#/LFfWA" rel="noreferrer"><strong>benchmark</strong></a> running these two implementations against each other.</p> <hr> <p>As noted in the comment below by @ThomasLeduc and others, there could be an issue with the regular expression-based implementation if <code>search</code> contains certain characters which are reserved as <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions#Using_special_characters" rel="noreferrer">special characters in regular expressions</a>. The implementation assumes that the caller will escape the string beforehand or will only pass strings that are without the characters in the table in <em><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions#Using_special_characters" rel="noreferrer">Regular Expressions</a></em> (MDN).</p> <p>MDN also provides an implementation to escape our strings. It would be nice if this was also standardized as <code>RegExp.escape(str)</code>, but alas, it does not exist:</p> <pre><code>function escapeRegExp(str) { return str.replace(/[.*+?^${}()|[\]\\]/g, "\\$&amp;"); // $&amp; means the whole matched string } </code></pre> <p>We could call <code>escapeRegExp</code> within our <code>String.prototype.replaceAll</code> implementation, however, I'm not sure how much this will affect the performance (potentially even for strings for which the escape is not needed, like all alphanumeric strings).</p>
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    1. POHow to replace all occurrences of a string in JavaScript?
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    1. USPeter Mortensen
    1. USCory Gross
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    1. POHow to replace all occurrences of a string in JavaScript?
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    1. COMay i ask what the g character is for when replacing all occurance of a string?
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      1. USjonney
    2. COIt's an option for the regular expression engine to use when matching the expression. Specifically, the `global` option will match every instance of the given pattern. It can also be applied on the end of the expression like so: `/(.{3})/g`. The `g` modifier on the end of the previous expression corresponds to the same `g` used in my code.
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