Left Trim in Javascript

Question

Hey guys,

there are lots of scripts out there to trim a string in javascript, but none how to Left Trim String.

This is what I use to trim:

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

But I would like to change this a little and create a new function called leftTrim that only removes the leading space. My regex is pretty limited, so any help is much appreciated.

Cheers

Answer 1

Use:

String.prototype.leftTrim = function() {
 return this.replace(/^\s+/,"");
}

In the regex the:

• ^ means "from the beginning of the string"
• \s means whitespace character class
• + means one-or more (greedy)

so....

• ^\s+ means "one or more consecutive whitespace characters from the beginning of the class"

Note: The g flag at the end of your regex is unnecessary as the anchors (^ and $) explicitly define what will match. There cannot be multiple matches.

See https://developer.mozilla.org/en/Core_JavaScript_1.5_Reference/Global_Objects/RegExp for details on regex syntax in javascript

Answer 2

String.prototype.leftTrim = function() {
        return this.replace(/^\s+/,"");
}

Answer 3

Very simple, the regex needs a small change:

String.prototype.leftTrim = function() {
    return this.replace(/^\s+/,"");
}

See also:

• Faster JavaScript Trim
• Using Regular Expressions with JavaScript and ActionScript
• JavaScript RexExp object reference

Answer 4

I've already answered a similar question just a few moments ago, but here's my solution to your question.

String.prototype.trimLeft = String.prototype.trimLeft || function () {
    var start = -1;

    while( this.charCodeAt(++start) < 33 );

    return this.slice( start, this.length);
};

The above solution is based on Ariel Flesler fast trim function and the fact that Firefox 3.5 and above has a built-in trimLeft method on the String object.