CODEWITHSUNDEEP
javascriptfunctionfunction-call
Ilya
Ilya

Reputation: 29703

Javascript, execute function

I have next function 

  var hideAll = function() {
    // code  
    return ///...  
  };

And I am using this function like callback in another function.
When I am using it like 

function (params, hideAll) {}

all working well, but when I am using 

function (params, hideAll() ) {}

all not working well!

So my question is, what is difference between hideAll and hideAll() function executions?

Upvotes: 2

Views: 1158

Answers (4)

Christoph
Christoph

Reputation: 28095

Let's step back for a moment and assume you would call a method foo first like this:

foo(params, hideAll() ) {}

This uses the return value of hideAll as the value

whereas

foo(params, hideAll) {}

Uses the hideAll function itself as the value

However, what you actually tried to do is to declare a function like this:

function (params, hideAll() ) {}

That makes no sense. You can't declare a function with anything different from a parameter in the parameter list.

So while both forms are legal for function invocation (still with a total different meaning) the latter isn't legal for function declaration

Upvotes: 0

6502
6502

Reputation: 114579

In Javascript and in many other languages functions are "first class objects" and this means that you can call/execute a function but you can also store the function in a variable or in an array, or you can pass a function to another function.

Note that I'm not talking about passing the value resulting from calling a function... but the function itself. Consider:

function test10(f) {
    for (var i=0; i<10; i++)
        alert(f(i));
}

function square(x) { return x*x*; }
function cube(x) { return x*x*x; }

test10(square);
test10(cube);

The last two lines are passing a function (square and cube) as a parameter to function test10.

The () syntax tells Javascript that you want to make the call, and can be used not only with function names, but with any expression like variables or array elements... for example:

var f_arr = [square, cube];
for (var i=0; i<2; i++)
  alert(f_arr[i](i+42));  // Will call square(42) and cube(43)

Actually in Javascript the code

function square(x) {
  return x * x;
}

is not identical but similar to

square = function(x) {
    return x * x;
};

so defining a function is indeed close to assigning a variable

Upvotes: 0

Li0liQ
Li0liQ

Reputation: 11264

hideAll - this is a reference to the function
hideAll() - this is execution of the function, its result

function (params, hideAll) {} is a correct function definition,
whereas function (params, hideAll() ) {} is not - you are unable to call another function in function definition.

However you could still write the following valid code:

  var hideAll = function() {
    // code  
    return ///...  
  };  

  var functionWithCallback = function(callback){
      callback();
  }
  var closureReferringHideAll = function(){
      hideAll();
  }

  // The following two lines will do exactly the same in current context,
  // i.e. execute hideAll.
  functionWithCallback(hideAll);
  closureReferringHideAll();

Upvotes: 3

Ozerich
Ozerich

Reputation: 2000

hideAll() is not a function, it is result of execution function.

function hideAll(){
    return 0;
}

hideAll() - number 0

hideAll - function

Upvotes: 0

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