Can I intercept a function called directly?

Question

In this code I created a function called someFunction. Then I modified Function.prototype.apply and call methods. So instead of my function code is working I am running my interception code (which shows an alert). But neither "call" nor "apply" intercepts direct method call. Is it possiple to intercept this?

Function.prototype.call = function(){alert("call");}; Function.prototype.apply = function(){alert("apply");}; function someFunction(){} window.onload = function(){     someFunction.call(this); //call alert is shown     someFunction.apply(this); //apply alert is shown     someFunction(); //how can I intercept this? } 

Answer 1

You can only override a known function by setting another function in its place (e.g., you can't intercept ALL function calls):

(function () {     // An anonymous function wrapper helps you keep oldSomeFunction private     var oldSomeFunction = someFunction;      someFunction = function () {         alert("intercepted!");         oldSomeFunction();     } })(); 

Note that, if someFunction was already aliased/referenced by another script before it was changed by this code, those references would still point to the original function not be overridden by the replacement function.

Answer 2

Function.prototype.callWithIntercept = function () {     alert("intercept");     return this.apply(null, arguments); }; 

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var num = parseInt.callWithIntercept("100px", 10); 

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It is worth noting that in newer versions of JS, there are Proxy objects you can use: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy