how to access a local javascript var in greasemonkey

Question

it's been an hour I'm going crazy with this problem.

There is a page, with a javascript function:

<script>
  function foofunction(foo){
      dosomething(foo);
    }
</script>

I have replaced this function with a greasemonkey script:

var scriptCode = new Array();

scriptCode.push('function foofunction(foo){    ');
scriptCode.push('    dosomething(foo);             ');
scriptCode.push('    myinjectedcode;               ');
scriptCode.push('}'                                 );

var script = document.createElement('script');
script.innerHTML = scriptCode.join('\n');
scriptCode.length = 0;

document.getElementsByTagName('head')[0].appendChild(script);
//here I have to access to foo value

This works.

Now I have to access to foo value in my greasemonkey script, how can I?

Answer 1

Why are you making your JavaScript function inside a array? I'm assuming foofunction is a global function, why don't you just make a function inside window (or unsafeWindow , I think, for Greasemonkey)?

unsafeWindow.foofunction = function(foo){
    dosomething(foo);
    //myinjectedcode;
}

foo is a local variable, so it only exists inside the foofunction function. If you want access to it outside of that, you'd need to make it a global variable.

unsafeWindow.foofunction = function(foo){
    dosomething(foo);
    //myinjectedcode;
    unsafeWindow.myFoo = foo;
}
unsafeWindow.myFoo; // will be set to `foo`, but only after `fooFunction` is ran

Problem with that is, myFoo will only be set after fooFunction is ran, and there's no good way for you to wait until then. I suggest making a "callback" function.

unsafeWindow.foofunction = function(foo){
    dosomething(foo);
    //myinjectedcode;
    unsafeWindow.myFooCallback(foo);
}
unsafeWindow.myFooCallback(foo){
    // this will be called with `foo` after `fooFunction` is ran.
}

But, this is kinda pointless as your injecting code into fooFunction anyway.

So, to answer your question, you cannot get the value of a local variable outside of the function. Since you're injecting code anyway, why don't you just put all code relating to foo inside fooFunction ?

Answer 2

如果您要在过程中跟踪值，我建议使用Firebug调试此类型的脚本，只需在脚本中所需的任何位置放置一个断点，并在其停止时将为您提供当前值关闭所有正在使用的变量。