Can I intercept a function called directly?

user_350127 0
Viewed 25536

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?
}
javascript
5 Answers

There is a chance you can intercept direct function call. This requires:

  • Either the function is created by Function.prototype.bind and you have to overwrite Function.prototype.bind before creating the function, or
  • The function is created from Function() (or new Function()) and you also have to overwrite Function function before creating the target function.

If neither of the above two can be met, the only way to intercept a direct call is to wrap the target function, which is the solution provided by AndyE https://stackoverflow.com/a/3406523/1316480

For a function that is created by function literal and is hidden in private scope, there is no way to intercept a direct call to it.

I have a blog post concludes all of these: http://nealxyc.wordpress.com/2013/11/25/intercepting-javascript-function/

user_13164800

Brilliant, love it :)

const originalApply = window.Function.prototype.apply;
window.Function.prototype.apply = function(){
    console.log("INTERCEPTING APPLY", arguments);
    return originalApply.call(this, ...arguments);
};
user_13475720
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