C# like trimStart method in JavaScript

trim-start.js

String.prototype.trimStart = function(c) {
    if (this.length == 0) return this;

    c = c ? c : ' ';
    var i = 0;
    for (; i < this.length && this.charAt(i) == c; i++);
    return this.substring(i);
}

// Example
"   hello world!".trimStart();