(() => {

  String.prototype.ensureStart = function(str = '') {
    if (!this.startsWith(str)) {
      return str + this;
    }

    return this.toString();
  }

  String.prototype.ensureEnd = function(str = '') {
    if (!this.endsWith(str)) {
      return this + str;
    }

    return this.toString();
  }

  String.prototype.isEmpty = function() {
    return this.length == 0;
  }


  String.prototype.truncate = function(n) {
    if (n < 4) {
      return '.'.repeat(n);
    }

    if (this.length < n) {
      return this.toString;
    }

    let foundedSpace = this.lastIndexOf(' ');

    if (foundedSpace != -1) {
      return str.substring(0,foundedSpace) + '...';
    } else {
      return str.substring(0, n - 3 ) + '...';
    }
  }

  String.format = function(str, ...params) {
      params.forEach((key, index) => {
        str = str.replace(`{${index}}`, key);
      })
  }

})();