我将一个函数（本身具有一个参数）作为参数传递给另一个函数，以及如何获取该参数

Question

I passed a function(which itself has a parameter let's say para) as a parameter into another function function b() and how to get the parameter para.

here is the simple example

<input type="button" onclick="sometest3()" value="Run test">

<script>
function sometest3() {

    // pass an anonymous function as a parameter which has
    // its own parameter "client"
    sometest('connection',function(client){client.getInfo();}) 
}


function sometest(eve,func) {

     // get this function's parameter which is "client" and pass
     // a reference of sometest2 to it. so in the callback I can use
     client.getInfo(); 
}


function sometest2() {
   this.getInfo=function (){alert("get it");};
}
</script>

Answer 1

You can't given the code you've posted. The anonymous function passed to sometest is held as a local variable that is inaccessible to functions outside its scope.

If you want sometest to access client , you must pass it, the following uses local variable:

function sometest3() {

    var client = {getInfo: function(){ /* whatever */}};

    sometest('connection', function(client){client.getInfo();}, client);
}


function sometest(eve, func, client) {

    // The client object has been passed from sometest3
    func(client);

}

Or you could make it available to both functions in a closure or global variable, or property of some object accessable to both functions (essentially these same thing). Your choice.

eg using a closure:

var foo = (function() {
    var client = {getInfo: function(){ /* whatever */}};
    return {
        sometest3: function() {
            foo.sometest('connection', function(obj){obj.getInfo();}, client);
        },

        sometest: function(eve, func, client) {
            // The client object has been passed from sometest3
            func(client);
        }
    };
}());

Then call it as foo.sometest3() .

Edit

Added call

Answer 2

If you want to know how many arguments are named in a function func you can check func.length . And this doesn't mean that you can't pass more or less arguments to that function, of course, but only how many of them are stored in local scoped variables.

But if you want to know the names of those variables the best thing to do is to convert the function to a string and get its declaration:

var parms = String(func)
        .match(/function[^\(]*\(([^\)]*)/)[1]
        .split(/\s*,\s*/);

(Mind you that putting comments between the function keyword and its declaration may mess up this method.)

That being said, I fail to see how this can be useful for you...