str.js

String.prototype.repr = function(n){
    return Array(n + 1).join(this);
}

String.prototype.lpad = function(/* Int */ length, /* String */ pad){
    // summary: left pad this string to become `length` using an optional `pad` character
    return (pad || " ").repr(length - this.length) + this;
}

String.prototype.rpad = function(length, pad){
    return this + (pad || " ").repr(length - this.length);
}