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Baseline Widely available

This feature is well established and works across many devices and browser versions. Itâs been available across browsers since 2015å¹´7æ.

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function getVowels(str) {
  const m = str.match(/[aeiou]/gi);
  if (m === null) {
    return 0;
  }
  return m.length;
}

console.log(getVowels("sky"));
// äºæ³ãããçµæ: 0

æ§æ

null

null å¤ã¯ null ã¨ãããªãã©ã«ã§ãã null ã¯ undefined ã®ãããªã°ãã¼ãã«ãªãã¸ã§ã¯ãã®ããããã£ã§ã¯ããã¾ãããä»£ããã«ã null ã¯èå¥ã§ããªããã¨ãè¡¨ããå¤æ°ããªãã¸ã§ã¯ããæãã¦ããªããã¨ãç¤ºãã¾ãã API ã«ããã¦ã¯ãéå¸¸ã¯ãªãã¸ã§ã¯ããè¿ãããã¨ããã§ãé¢é£ãããªãã¸ã§ã¯ãããªãå ´åã« null ãããæ¸¡ããã¾ãã

// foo ãåå¨ãããå®ç¾©ãåæåãããã¦ããªãå ´å:
foo; // ReferenceError: foo is not defined

// foo ãåå¨ãã¦ããããåãå¤ãæããªãå ´å:
const foo = null;
foo; // null

ä¾

`null` ã¨ `undefined` ã®éã

null ã undefined ããã§ãã¯ããéã¯ãçä¾¡ (==) ã¨ å³å¯çä¾¡ (===) æ¼ç®åã®éã ã«æ³¨æãã¦ãã ããï¼åèã§ã¯åå¤æãè¡ããã¾ãï¼ã

typeof null; // "object" (æ´å²çãªçç±ã§ "null" ã§ã¯ããã¾ãã)
typeof undefined; // "undefined"
null === undefined; // false
null == undefined; // true
null === null; // true
null == null; // true
!null; // true
Number.isNaN(1 + null); // false
Number.isNaN(1 + undefined); // true