Left Trim in Javascript

https://stackoverflow.com/questions/1593859

22-09-2019
|

Question

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

Solution

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

OTHER TIPS

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.

to keep this updated:

ES 10:

with ES10 comes the trimStart functionality.

a synonym for it is trimLeft.

const greeting = '   Hi!   ';
console.log(greeting); 
// "   Hi!   "
console.log(greeting.trimStart()); 
// "Hi!   "
console.log(greeting.trimLeft()); 
// "Hi!   "

ES6:

an ES6 version could be:

function trimLeft(string) {
  const first = [...string].findIndex(char => char !== ' ');
  return string.substring(first, string.length);
}

console.log(trimLeft("   Hi!   ", chars));
// "Hi!   "

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

Very simple, the regex needs a small change:

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