Javascript callback functions execution

Question

I'm not sure the correct term for this. But I want to write a function that accepts another function and execute it. For eg.

function test(data, aFunc) {
   var newData = data + " Shawn";

   aFunc.call(newData);
}

test("hello", function(data){
   alert(data);
});

Data is supposed to contain "hello Shawn" string. Help me rewrite this the correct way please.

Answer 1

Looks fine but you can just change

aFunc.call(newData);

to

aFunc(newData);

Answer 2

You were close. The first argument to "call" is the "scope" argument. In this case, it doesn't matter what it is, because you're not using "this" anywhere in your anonymous function, so any value will suffice.

function test(data, aFunc) {
   var newData = data + " Shawn";

   aFunc.call(this, newData);
}

test("hello", function(data){
   alert(data);
});

Answer 3

The first argument of the call method is used to set the this keyword (the function context) explicitly, inside the invoked function, e.g.:

function test(data, aFunc) {
   var newData = data + " Shawn";

   aFunc.call(newData);
}

test("hello", function () {
   alert(this); // hello Shawn
});

If you want to invoke a function without caring about the context (the this keyword), you can invoke it directly without call:

function test(data, aFunc) {
   var newData = data + " Shawn";

   aFunc(newData); // or aFunc.call(null, newData);
}

test("hello", function (data) {
   alert(data);
});

Note that if you simply invoke a function like aFunc(newData); or you use the call or apply methods with the this argument set as null or undefined, the this keyword inside the invoked function will refer to the Global object (window).