FAQ Topic - How do I trim whitespace? (2009-12-10)

[Asen Bozhilov]

        return function(){
            return this.replace(reTrim,"$1");

^^^^
Should be explicit cast `this' value ToString, because in ES5:

The trim function is intentionally generic; it does not require that
its this value be a String object. Therefore, it can be transferred to
other kinds of objects for use as a method.

String.prototype.trim.call([' x', 'x ']).length;

 

[Garrett Smith]

It seems simpler and easier to see:

if(!String.prototype.trim) { }

Than:

if(typeof String.prototype.trim !== "undefined") { }

The former is shorter and puts the negation first.

In ECMA5 15.5.4.20 String.prototype.trim refer to object which
internal [[Prototype]] refer Function.prototype. Internal have
[[Call]] and [[Construct]] methods.

While it is true that String.prototype.trim is a function, and it is
true that it has Function.prototype in its prototype chain, neither
String.prototype.trim nor Function.prototype implement [[Construct]].

Any of the following list should result in TypeError:-

new "".trim();
new Function.prototype();
new parseInt
new [].slice

Mozilla's results show an aberration.

But if i explicit define trim function and assign to
String.prototype.trim i don't need from all of that test before i call
`trim'. Because of that i will be use:

if (typeof String.prototype.trim !== 'function')
{
String.prototype.trim = function()
{
//do trim
};
}

So in my code i can directly use:

str.trim();

Without feature test every time when i call `trim' method.

Of course the feature test and patch should be done only once.

 

[Garrett Smith]

return function(){
return this.replace(reTrim,"$1");

^^^^
Should be explicit cast `this' value ToString, because in ES5:

The trim function is intentionally generic; it does not require that
its this value be a String object. Therefore, it can be transferred to
other kinds of objects for use as a method.

String.prototype.trim.call([' x', 'x ']).length;

The FAQ should be accordingly changed to:-

if(!String.prototype.trim) {
String.prototype.trim = function() {
// The trim function is intentionally generic (s 15.5.4.20).
return (this+"").replace(/^\s+|\s+$/g, "");
};
}