returnTrue and returnFalse functions in jQuery source

Question

I can\'t help but notice there are two seemingly useless functions in the source code of jQuery (For v1.9.1, it\'s line 2702 and line 2706):

function returnTrue(         


        

Answer 1

If an object property, function argument, etc expects a function you should provide a function not a boolean.

For example in vanilla JavaScript:

var a = document.createElement("a");
a.href = "http://www.google.com/";
/*
 * see https://developer.mozilla.org/en-US/docs/DOM/element.onclick
 * element.onclick = functionRef;
 * where functionRef is a function - often a name of a function declared 
 * elsewhere or a function expression.
 */
a.onclick = true;                        // wrong
a.onclick = returnTrue;                  // correct
a.onclick = function() { return true; }; // correct

Also, writing:

someProperty: returnTrue,

Is more convenient than writing:

someProperty: function(){
    return true;
},

Especially since they are called quite often.