difference between String.prototype.trim.call(text) and text.trim()

Question

Looking into jQuery's source:

// Use native String.trim function wherever possible
trim: trim && !trim.call("\uFEFF\xA0") ?
    function( text ) {
        return text == null ?
            "" :
            trim.call( text );
    } :

    // Otherwise use our own trimming functionality
    function( text ) {
        return text == null ?
            "" :
            ( text + "" ).replace( rtrim, "" );
    },

is there a reason Why they use trim.call(text) instead of text.trim()? Thanks a lot!!

UPDATE:

Right this way it won't throw exceptions if the argument is not a string. But according to jQuery's doc, the argument is supposed to be a string so if user uses it wrong, should it throw an exception (otherwise user might not notice what's wrong)?

And to Nathaniel Currier: the mothod is jQuery.trim() not jQuery.fn.trim() so it is not chained.

Answer 1

I'm not sure that this was their design rationale, but using call() will work with objects that are not strings:

var a = [1, 2, 3];
var b = String.prototype.trim.call(a); // same result as b = '1,2,3'
var c = a.trim(); // => generates TypeError

Notice that their polyfill coerces text to a string with ( text + "" ) .

Answer 2

String.trim() is not available in all (older) browsers so they use native if available (as its faster) or their own implementation if not...

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/Trim

also see this for information about how Function.prototype.call() behaves https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/call

Answer 3

当text不是字符串时， text.trim()将抛出错误（ TypeError: .... has no method 'trim' ），而String.prototype.trim.call(text)则不会。