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    <p>You cannot stop the variable <code>g1</code> from being reassigned on all browsers. Some browsers would allow you to define <code>g1</code> as a <a href="https://developer.mozilla.org/en/JavaScript/Reference/Statements/const" rel="nofollow noreferrer">constant</a> thus:</p> <pre><code>const g1 = G(f1); </code></pre> <p>which would prevent the name <code>g1</code> from being rebound, and you can use <code>Object.defineProperty</code> to define a <a href="https://stackoverflow.com/questions/366047/can-read-only-properties-be-implemented-in-pure-javascript">read-only</a> global property of <code>window</code> on others, but in general, there are no <code>const</code> definitions in JavaScript.</p> <p>To make it clearer, consider two scenarios:</p> <p>(1) An attacker can run code in the scope in which <code>f1</code> is declared, and then other code reads <code>f1</code>.</p> <pre><code>var f1 = ...; // You define f1 f1 = function () { return false; }; // Attacker code runs doSomethingWith(f1()); // Naive code reads f1 and calls it. </code></pre> <p>The attacker succeeds in this case in confusing the naive code because they changed the value at <code>f1</code>.</p> <p>(2) An attacker runs code in the scope after <code>f1</code> has been read.</p> <pre><code>var f1 = ...; // You define f1 // Cautious code reads and stores f1 in a safe place for later use. (function () { var f = f1; setTimeout(0, function () { doSomethingWith(f()); }); })(); f1 = function () { return false; }; // Attacker code runs. </code></pre> <p>The attacker fails in this case because the cautious code read the value of <code>f1</code> before the attacker changed the value stored at <code>f1</code>, so the private <code>f</code> continues to return <code>true</code>.</p>
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    1. PO is an instance of a javascript function object immutable
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    1. COserious typo in the code.. i've edited my question: it is not the code you assumed it to be.. but rather: `function G(f){return function(){return f;}}`
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    2. CO@Pacerier, removed bit about definition of G since it looks like your new definition of G will do what you want. The rest of the post, about how to make the name `g1` always point (modulo masking) to the same function instance is still relevant.
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    3. COso even after i've passed the instance of the function called `f1` into an attacker's script, he can do whatever he want to `f1` but at the end of his script i can still call `f1` and say that it will 100% return me true?
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