JavaScriptでの型判別まとめ(typeof, Object.prototype.toString.call)

自分用メモ

型	値	typeof	toString.call
string	"", "abc", 'a', String(1)	string	[object String]
String	new String("")	object	[object String]
number	0, NaN, Infinity, Number('1')	number	[object Number]
Number	new Number(0)	object	[object Number]
bigint	1n, BigInt(1)	bigint	[object BigInt]
Bigint	Object(1n)	object	[object BigInt]
boolean	true, Boolean(0)	boolean	[object Boolean]
Boolean	new Boolean(true)	object	[object Boolean]
symbol	Symbol(1)	symbol	[object Symbol]
Symbol	Object(Symbol(1))	object	[object Symbol]
null	null	object	[object Null]
undefined	undefined	undefined	[object Undefined]
array	[]	object	[object Array]
object	{}	object	[object Object]
function	() => {}	function	[object Function]
Map	new Map()	object	[object Map]
Set	new Set()	object	[object Set]
Date	new Date()	object	[object Date]
Error	new Error()	object	[object Error]

開発者ツールのコンソールで試せるコード

console.log('string: ', typeof 'a', Object.prototype.toString.call('a'))
console.log('String: ', typeof new String(""), Object.prototype.toString.call(new String("")))
console.log('number: ', typeof 0, Object.prototype.toString.call(0))
console.log('Number: ', typeof new Number(0), Object.prototype.toString.call(new Number(0)))
console.log('boolean: ', typeof true, Object.prototype.toString.call(true))
console.log('Boolean: ', typeof new Boolean(true), Object.prototype.toString.call(new Boolean(true)))
console.log('bigint: ', typeof 1n, Object.prototype.toString.call(1n))
console.log('BigInt: ', typeof Object(1n), Object.prototype.toString.call(Object(1n)))
console.log('symbol: ', typeof Symbol(1), Object.prototype.toString.call(Symbol(1)))
console.log('Symbol: ', typeof Object(Symbol(1)), Object.prototype.toString.call(Object(Symbol(1))))
console.log('null: ', typeof null, Object.prototype.toString.call(null))
console.log('undefined: ', typeof undefined, Object.prototype.toString.call(undefined))
console.log('array: ', typeof [], Object.prototype.toString.call([]))
console.log('object: ', typeof {}, Object.prototype.toString.call({}))
console.log('function: ', typeof (() => {}), Object.prototype.toString.call((() => {})))
console.log('Map: ', typeof new Map(), Object.prototype.toString.call(new Map()))
console.log('Set: ', typeof new Set(), Object.prototype.toString.call(new Set()))
console.log('Date: ', typeof new Date(), Object.prototype.toString.call(new Date()))
console.log('Error: ', typeof new Error(), Object.prototype.toString.call(new Error()))

toString.callを使うなら、以下のような感じで判別に使える

const getType = (a: any): string =>
  Object.prototype.toString.call(a).replace('[object ', '').replace(']', '')

if (getType('hoge') === 'String') console.log('string')
// -> string

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参考