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.

e.g. 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