I was trying to understand how jQuery's cross-browser events work, when I noticed these two functions in the source code:

function returnTrue() {
    return true;

function returnFalse() {
    return false;

Further down in the code these are used like:

if ( fn === false ) {
    fn = returnFalse;    <--- here
} else if ( !fn ) {
    return elem;


// Events bubbling up the document may have been marked as prevented
// by a handler lower down the tree; reflect the correct value.
this.isDefaultPrevented = src.defaultPrevented ||
    src.defaultPrevented === undefined &&

    // Support: Android <=2.3 only
    src.returnValue === false ?
returnTrue :    <--- here


jQuery.Event.prototype = {
    constructor: jQuery.Event,
    isDefaultPrevented: returnFalse,    <--- here
    isPropagationStopped: returnFalse,
    isImmediatePropagationStopped: returnFalse,
    isSimulated: false,

    preventDefault: function() {
        var e = this.originalEvent;

        this.isDefaultPrevented = returnTrue;    <--- here

My question is: Why one would need such functions in a dynamic language like JavaScript, where you can easily write something like below:

if ( 'function' === typeof fn ) {
    return fn.apply( this, arguments );

else if ( 'boolean' === typeof fn ) {
    return fn;

Is this a code-smell? Or are these valid practices for perhaps a cleaner-code-base with fewer conditional statements? Or is it just a narrow case where, for example, the browser expects a function to invoke which would then return a boolean value, therefore these two functions are just for saving developer's time and keystrokes?

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