有没有办法查看（匿名）函数？

Question

In JavaScript, let's say you have:

function doSomething(callback) {
    if (callback instanceof Function) callback();
}

doSomething(function() {
    alert('hello world');
});

Is there a way to check what is inside 'callback' (like, the fact that alert() is called) from doSomething() ? Something like:

function doSomething(callback) {
    alert(callback.innards().indexOf('alert('));
}

I'm just curious

Answer 1

Function.prototype.toString() gives an implementation-dependent representation of the function . However built-in functions will return something like:

function Array() {
   /* [native code] */
}

and host methods can return anything, even throw an error. So the strict answer is yes, maybe. But in a practical sense, it is not reliable.

Answer 2

Some browsers support toString() on functions.

function doSomething(callback) {
    console.log( callback.toString().indexOf('alert(') )
    if (callback instanceof Function) callback();
}

Answer 3

You should be able to say:

alert( callback.toString().indexOf('alert(') );

However that won't distinguish between the beginning of a function alert( , the beginning of a function myspecialalert( , and the text "alert(" if it happens to be in a string literal - so you may need to do a bit of parsing.

Not sure how cross-browser this is, but in Firefox at least .toString() returns the whole text of the function including the word "function" and the parameter list.

Answer 4

callback.toString().indexOf('alert(');

或者做正则表达式匹配，如：

/alert *\(/.test(callback.toString());