Baseline Widely available
å ç® (+
) æ¼ç®åã¯ãæ°å¤ãªãã©ã³ãã®åè¨ã¾ãã¯æååã®é£çµãçæãã¾ãã
console.log(2 + 2);
// äºæ³ãããåºå: 4
console.log(2 + true);
// äºæ³ãããåºå: 3
console.log("hello " + "everyone");
// äºæ³ãããåºå: "hello everyone"
console.log(2001 + ": A Space Odyssey");
// äºæ³ãããåºå: "2001: A Space Odyssey"
æ§æ 解説
æ¼ç®å +
ã¯æ°å¤ã®å ç®ã¨æååã®é£çµã¨ãã 2 ã¤ã®ç°ãªãæä½ã®ããã«ãªã¼ãã¼ãã¼ãããã¦ãã¾ããè©ä¾¡ããã¨ããã¾ã両æ¹ã®ãªãã©ã³ããããªããã£ãã«å¤æãã¾ãããã®å¾ã 2 ã¤ã®ãªãã©ã³ãã®åããã¹ãããã¾ãã
TypeError
ä¾å¤ãçºçãã¾ããæååã®é£çµã¯ãã³ãã¬ã¼ããªãã©ã«ã String.prototype.concat()
ã¨ç価ã ã¨æãããã¡ã§ãããããã§ã¯ããã¾ãããå ç®ã¯ valueOf()
ãåªå
çã«å¼ã³åºãã¦ãå¼ãããªããã£ãã«å¤æãã¾ãã䏿¹ããã³ãã¬ã¼ããªãã©ã«ã¨ concat()
㯠toString()
ãåªå
çã«å¼ã³åºããå¼ãæååã«å¤æãã¾ããå¼ã [Symbol.toPrimitive]()
ã¡ã½ãããæã£ã¦ããå ´åãæååé£çµã¯ "default"
ããã³ãã¨ãã¦ãããå¼ã³åºãã¾ããããã³ãã¬ã¼ããªãã©ã«ã¯ "string"
ã使ç¨ãã¾ããããã¯ãæåå表ç¾ã¨ããªããã£ã表ç¾ãç°ãªããªãã¸ã§ã¯ããä¾ãã°ã Temporal
ã®ããã« valueOf()
ã¡ã½ããããã¹ã¦ä¾å¤ãçºçãããããªãªãã¸ã§ã¯ãã«ã¨ã£ã¦éè¦ã§ãã
const t = Temporal.Now.instant();
"" + t; // TypeError ãçºç
`${t}`; // '2022-07-31T04:48:56.113918308Z'
"".concat(t); // '2022-07-31T04:48:56.113918308Z'
"" + x
ã使ç¨ãã¦æååã«å¤æãè¡ããªããã¨ããå§ããã¾ãã
ãã以å¤ã®æååã§ã¯ãªããé·æ´æ°ã§ã¯ãªãå¤ã¯æ°å¤ã«å¤æããã¾ãã
true + 1; // 2
false + false; // 0
é·æ´æ°ã使ç¨ããå ç®
é·æ´æ°ã¨æ°å¤ã®ãªãã©ã³ããæ··å¨ããããã¨ã¯ã§ãã¾ããã
1n + 2; // TypeError: Cannot mix BigInt and other types, use explicit conversions
2 + 1n; // TypeError: Cannot mix BigInt and other types, use explicit conversions
"1" + 2n; // TypeError: Cannot mix BigInt and other types, use explicit conversions
é·æ´æ°ã¨é·æ´æ°ä»¥å¤ã§å ç®ãè¡ãã«ã¯ãã©ã¡ããã®ãªãã©ã³ãã夿ãã¦ãã ããã
1n + BigInt(2); // 3n
Number(1n) + 2; // 3
æååã使ç¨ããå ç®
ãªãã©ã³ãã®ä¸æ¹ãæååã®å ´åããã䏿¹ãæååã«å¤æãããããããé£çµããã¾ãã
"foo" + "bar"; // "foobar"
5 + "foo"; // "5foo"
"foo" + false; // "foofalse"
"2" + 2; // "22"
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