String.prototype.concat()
concat()方法将字符串参数连接到调用字符串, 并返回一个新字符串。
var str1 = 'Hello';
var str2 = 'World';
console.log(str1.concat(...[' ', 'mao', '_', 'si', 'yu']));
// expected output: "Hello mao_siyu"
console.log(str1.concat([' ', 'mao', '_', 'si', 'yu']));
// expected output: "Hello ,mao,_,si,yu"
console.log(str2.concat(' ', str1));
// expected output: "World Hello"