String.prototype.concat()

Baseline

20157

concat() String

const str1 = "Hello";
const str2 = "World";

console.log(str1.concat(" ", str2));
// : "Hello World"

console.log(str2.concat(", ", str1));
// : "World, Hello"

concat(str1)
concat(str1, str2)
concat(str1, str2, /* , */ strN)

str1, , strN: str 1 String.prototype.concat() Array.prototype.concat()

concat()

concat() / (+, +=) concat() +

concat()

const hello = "";
console.log(hello.concat("", ""));
// Hello, Kevin. Have a nice day.

const greetList = ["", " ", "", "!"];
"".concat(...greetList); // " !"

"".concat({}); // "[object Object]"
"".concat([]); // ""
"".concat(null); // "null"
"".concat(true); // "true"
"".concat(4, 5); // "45"


ECMAScript 2027 LanguageSpecification # sec-string.prototype.concat

Array.prototype.concat()
(+)

MDN

MDN 2025822

GitHub

String
1. String()
1. length
Object/Function
1. __proto__
2. constructor