(function Extend() {

    String.prototype.ensureStart = function (str) {
        let startsWith = true;
        for (let i = 0; i < str.length; i++) {
            startsWith = str[i] === this[i];
        }

        return startsWith ? '' + this : str + this;
    };

    String.prototype.ensureEnd = function (str) {
        let endsWith = true;
        for (let i = 0; i < str.length; i++) {
            endsWith = str[str.length - 1 - i] === this[this.length - 1 - i];
        }

        return endsWith ? '' + this : this + str;
    };

    String.prototype.isEmpty = function () {
        return str === '';
    };

    String.prototype.truncate = function (n) {
        if (this.length <= n){
            return this + "";
        }else {
            if (!/\s+/.test(this)){
                if (n < 4){
                    return ".".repeat(n);
                }
                return this.slice(0, n - 3) + "...";
            }else {
                if (n < 4) {
                    return ".".repeat(n);
                }
                return this.slice(0, n - 3) + "...";
            }
        }
    };

    String.prototype.format = function (str1, str2, str3) {
        if (str2 !== '' || str2 !== undefined){
            str1.replace('{0}', str2);
        }

        if (str3 !== '' || str3 !== undefined){
            str1.replace('{1}', str3);
        }

        return str1;
    }
})();