å ç®ä»£å¥æ¼ç®å (+=)

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let a = 2;
let b = "hello";

console.log((a += 3)); // å ç®
// äºæ³ãããçµæ: 5

console.log((b += " world")); // çµå
// äºæ³ãããçµæ: "hello world"

x += y

x += y ã¯ x = x + y ã¨åçã§ãããå¼ x ã¯ä¸åº¦ããè©ä¾¡ããã¾ããã

let bar = 5;
bar += 2; // 7

ããä»¥å¤ã®æååã§ãé·æ´æ°ã§ããªãå¤ã¯ãæ°å¤ã«å¤æããã¾ãã

let baz = true;
baz += 1; // 2
baz += false; // 2

let x = 1n;
x += 2n; // 3n

x += 1; // TypeError: Cannot mix BigInt and other types, use explicit conversions

let foo = "foo";
foo += false; // "foofalse"
foo += "bar"; // "foofalsebar"

let bar = 5;
bar += "foo"; // "5foo"

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ECMAScriptÂ® 2027 LanguageÂ Specification # sec-assignment-operators