How can we know if a function is called from console or from source code

Question

I want to know if there is a way to check if a javascript function is being called from console of the browser or from source code.

I defined a function that can ch

Answer 1

In Chrome the console always calls intermediate JavaScript functions, in Firefox the call comes directly from native code. As a consequence, you can inspect arguments.callee.caller in Chrome but in Firefox it will always be null. Safari behaves the same as Firefox here, so inspecting the caller is really a trick that only works in Chrome.

What you can check nevertheless is Error.stack property. The following function works in Firefox, Chrome and even Safari:

function fromConsole()
{
    var stack;
    try
    {
       // Throwing the error for Safari's sake, in Chrome and Firefox
       // var stack = new Error().stack; is sufficient.
       throw new Error();
    }
    catch (e)
    {
        stack = e.stack;
    }
    if (!stack)
        return false;

    var lines = stack.split("\n");
    for (var i = 0; i < lines.length; i++)
    {
        if (lines[i].indexOf("at Object.InjectedScript.") >= 0)
            return true;   // Chrome console
        if (lines[i].indexOf("@debugger eval code") == 0)
            return true;   // Firefox console
        if (lines[i].indexOf("_evaluateOn") == 0)
            return true;   // Safari console
    }
    return false;
}

This will walk up the stack until it finds an entry corresponding to the console. This means that fromConsole() doesn't need to be called directly, there can be any number of other function calls in between. Still, it can easily be tricked, e.g. by using setTimeout():

setTimeout(fromConsole, 0);

Here the caller will be the native timeout handler, nothing pointing to the console any more.