Why does my function execute when I push it onto a JS array?

Question

I ran across this problem when trying to populate a JS array for some animation I'm doing....the following Javascript function is invoked when I click a link within my web page for testing purposes:

function testing()
{
    var funcArray = [];
    var testFunc = function(){console.log("test function");}

    funcArray.push(function(){console.log("hello there");});
    funcArray.push(testFunc());
}

When this executes, I get "test function" to appear in the JS console, but not "hello there". Why does pushing the predefined testFunc cause output, but not the inline function in the first push?

Remove the function brackets. Only push the name, funcArray.push(testFunc); — Dave Chen
– Dave Chen, Commented Jul 18, 2015 at 20:48

doldt · Accepted Answer · 2015-07-18 20:48:41Z

6

Because you're calling it.

funcArray.push(testFunc());

calls testFunc, then pushes the result of that call into funcArray. You probably want funcArray.push(testFunc); (note the omitted ()), which just pushes the function reference to that array.

answered Jul 18, 2015 at 20:48

doldt

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Comments

Luca Schimweg · Accepted Answer · 2015-07-18 20:49:56Z

1

Because you execute it in funcArray.push(testFunc());... What you want is funcArray.push(testFunc); Because testFunc() executes the Function, takes the return and pushes it to the Array, while testFunc takes the actual function to push.

answered Jul 18, 2015 at 20:49

Luca Schimweg

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