Here you can find the source of contains(str)
String.prototype.contains = function(str) { return this.indexOf(str) > -1; };
String.prototype.contains = function(search) return this.toLowerCase().indexOf(search.toLowerCase()) !== -1; };
String.prototype.contains = function (searchFor) { return String.prototype.indexOf.call(this, String(searchFor)) !== -1; };
String.prototype.contains = function(searchString){ return (this.indexOf(searchString) != -1); };
String.prototype.contains = function (searchString) { return !!~this.indexOf(searchString); };
String.prototype.contains = function(str) { return this.indexOf(str) != -1; }; module.exports = { isNullOrEmpty: function(str){ return str == null || str == ''; };
String.prototype.contains = function(str) { return this.indexOf(str) !== -1; };
String.prototype.contains = function(str) { if (typeof str !== 'string') return false; return this.indexOf(str) !== -1; };
String.prototype.contains = function(str) { return this.toLowerCase().indexOf(str.toLowerCase()) > -1; };
String.prototype.contains = function(str) return this.indexOf(str) != -1; };