how can I call a JS self-executing function later if I want?

Question

I am trying to write a function that executes immediately but can also be later like:

var test = function (e){ console.log('hello'+e); }();
$('#some_element').click(function(e){
    test(' world');
});

where in this case, the results I would want would be:

helloundefined
hello world

I am not grasping why calling test later returns 'test is not a function'.

Answer 1

You define test like this:

var test = function (e){ console.log('hello'+e); }();

This creates a closure and then immediately calls it. Since there's no explicit return in the closure, it returns undefined . Now test contains undefined . Later, in the closure passed to click , it tries to call test . test is still undefined . You end up doing something like this:

undefined(' world');

You say you wanted it to output this:

helloundefined
hello world

In that case, you can do this:

var test = function test(e) { console.log('hello'+e); return test; }();

As a side effect, it also makes test chainable, so you could do this:

test(" world")(" stack overflow")(" internet");

And the result (excluding the first helloundefined ) would be:

hello world
hello stack overflow
hello internet

Answer 2

var test = function (e){ console.log('hello'+e); }();

Those parens at the end mean that test is the result of evaluating a function call (in other words the return value of the function), not the function itself.

Try this:

var testFunc = function (e){ console.log('hello'+e); };
testFunc();
$('#some_element').click(function(e){
    testFunc(' world');
});

Answer 3

var test;
(test = function( e ) { console.log('hello'+e); } )(); //helloundefined

test( ' world' ); //hello world

Answer 4

You're assigning the return value of the function to test , not the function itself. I don't think you can use the self-executing shortcut if you also want to assign it to a variable. You'll need to do:

var test = function (e){ console.log('hello'+e); };
test();
$('#some_element').click(function(e){
    test(' world');
});