javascript - Should i modify the prototype of String? - Stack Overflow

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I was about to create a trim function in javascript, but as i don't want to reinvent the wheel i googled for this method.
I found this link .php

The Solution it provided is:

String.prototype.trim = function() {
    return this.replace(/^\s+|\s+$/g,"");
}
String.prototype.ltrim = function() {
    return this.replace(/^\s+/,"");
}
String.prototype.rtrim = function() {
    return this.replace(/\s+$/,"");
}

also it says if you don'y wnt to change the prototype of String then use this:

function trim(stringToTrim) {
    return stringToTrim.replace(/^\s+|\s+$/g,"");
}
function ltrim(stringToTrim) {
    return stringToTrim.replace(/^\s+/,"");
}
function rtrim(stringToTrim) {
    return stringToTrim.replace(/\s+$/,"");
}

I would like to know in what scenario one should not modify the prototype of String or say any object.

I was about to create a trim function in javascript, but as i don't want to reinvent the wheel i googled for this method.
I found this link http://www.somacon./p355.php

The Solution it provided is:

String.prototype.trim = function() {
    return this.replace(/^\s+|\s+$/g,"");
}
String.prototype.ltrim = function() {
    return this.replace(/^\s+/,"");
}
String.prototype.rtrim = function() {
    return this.replace(/\s+$/,"");
}

also it says if you don'y wnt to change the prototype of String then use this:

function trim(stringToTrim) {
    return stringToTrim.replace(/^\s+|\s+$/g,"");
}
function ltrim(stringToTrim) {
    return stringToTrim.replace(/^\s+/,"");
}
function rtrim(stringToTrim) {
    return stringToTrim.replace(/\s+$/,"");
}

I would like to know in what scenario one should not modify the prototype of String or say any object.

• javascript
• prototype

Share Improve this question Follow asked Nov 9, 2009 at 11:18 Rakesh JuyalRakesh Juyal 36.8k7474 gold badges178178 silver badges217217 bronze badges

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3 Answers 3

Sorted by: Reset to default 8

The trim functions are to be standardised in ECMAScript Fifth Edition, as well as already being present in some browsers. So:

1. Yes, adding them to the prototype is totally appropriate, but

2. You shouldn't add them to the prototype if they're already there, as you'll just be replacing a fast native-code function with a slow JavaScript one.

It is also typically marginally faster to do trim as two replaces:

// Add ECMA262-5 string trim if not supported natively
//
if (!('trim' in String.prototype)) {
    String.prototype.trim= function() {
        return this.replace(/^\s+/, '').replace(/\s+$/, '');
    };
}

In general - do not modify a prototype of buildin objects. But ofcourse you can add your handy function.

And always check before you add:

//pre-1.6 javascript
if (!Array.prototype.indexOf) {
    Array.prototype.indexOf = function(elt) {
        var len = this.length >>> 0;
        var from = Number(arguments[1]) || 0;
        from = (from < 0) ? Math.ceil(from) : Math.floor(from);
        if (from < 0)
            from += len;
        for (; from < len; from++) {
            if (from in this && this[from] === elt)
                return from;
        }
        return -1;
    };
}

This way you didn't overwrite mush faster buildin function that may bee available sometime...

For this kind of very useful utility function, I'd say you can modify the prototype. But you should be aware that the function may already exist natively in a few browsers, so you should check it : https://developer.mozilla/En/Core_JavaScript_1.5_Reference/Objects/String

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