JavaScript配列チェック方法

JavaScriptで変数が配列かどうかチェックする方法

JavaScriptでは、変数が配列かどうかをチェックする方法はいくつかあります。以下はそのうちのいくつかです。

Array.isArray() メソッド

最もシンプルで推奨される方法です。

const arr = [1, 2, 3];
const str = "hello";

if (Array.isArray(arr)) {
  console.log("arr is an array");
} else {
  console.log("arr is not an array");
}

if (Array.isArray(str)) {
  console.log("str is an array");
} else {
  console.log("str is not an array");
}

instanceof 演算子

オブジェクトのプロトタイプチェーンをチェックします。

const arr = [1, 2, 3];
const str = "hello";

if (arr instanceof Array) {
  console.log("arr is an array");
} else {
  console.log("arr is not an array");
}

if (str instanceof Array) {
  console.log("str is an array");
} else {
  console.log("str is not an array");
}

typeof 演算子 (ただし注意が必要)

typeof 演算子は配列を object として返します。そのため、厳密なチェックには適していません。

const arr = [1, 2, 3];
const str = "hello";

if (typeof arr === "object") {
  console.log("arr is an array");
} else {
  console.log("arr is not an array");
}

if (typeof str === "object") {
  console.log("str is an array");
} else {
  console.log("str is not an array");
}

const arr = [1, 2, 3];
const str = "hello";

if (Array.isArray(arr)) {
  console.log("arr is an array");
} else {
  console.log("arr is not an array");
}

if (Array.isArray(str)) {
  console.log("str is an array");
} else {
  console.log("str is not an array");
}

const arr = [1, 2, 3];
const str = "hello";

if (arr instanceof Array) {
  console.log("arr is an array");
} else {
  console.log("arr is not an array");
}

if (str instanceof Array) {
  console.log("str is an array");
} else {
  console.log("str is not an array");
}

const arr = [1, 2, 3];
const str = "hello";

if (typeof arr === "object") {
  console.log("arr is an array");
} else {
  console.log("arr is not an array");
}

if (typeof str === "object") {
  console.log("str is an array");
} else {
  console.log("str is not an array");
}

const arr = [1, 2, 3];
const str = "hello";

if (Array.isArray(arr)) {
  console.log("arr is an array");
} else {
  console.log("arr is not an array");
}

if (Array.isArray(str)) {
  console.log("str is an array");
} else {
  console.log("str is not an array");
}

const arr = [1, 2, 3];
const str = "hello";

if (arr instanceof Array) {
  console.log("arr is an array");
} else {
  console.log("arr is not an array");
}

if (str instanceof Array) {
  console.log("str is an array");
} else {
  console.log("str is not an array");
}

const arr = [1, 2, 3];
const str = "hello";

if (typeof arr === "object") {
  console.log("arr is an array");
} else {
  console.log("arr is not an array");
}

if (typeof str === "object") {
  console.log("str is an array");
} else {
  console.log("str is not an array");
}