js data types and their judgment method examples

js data types

Basic data types: number, string, boolean, undefined, null, Symbol,

Reference data type: object

NaN belongs to number;
Function, Array, Date are all objects;

Basic data types except null can be judged by typeof, and reference data types except Function return Object

let a = 1,
 b = '2',
 c = true,
 d = undefined,
 e = null,
 f = Symbol('f'),
 g = function () {},
 h = [],
 i = new Date()
console.log(typeof a)
console.log(typeof b)
console.log(typeof c)
console.log(typeof d)
console.log(typeof e)
console.log(typeof f)
console.log(typeof g)
console.log(typeof h)
console.log(typeof i)

View the output

You can see that the typeof of null is object. This is a historical bug. If you are interested, you can refer to "The history of "typeof null""

You can use the following method to determine null

function checkNull(num) {
 return num === null
}

The detailed type of object can be determined by Object.prototype.toString.call()

function checkObject(obj) {
 return Object.prototype.toString.call(obj)
}
console.log(checkObject(g))
console.log(checkObject(h))
console.log(checkObject(i))

You can see the output results

It can also be judged by the constructor constructor()

console.log(g.constructor === Function)
console.log(h.constructor === Array)
console.log(i.constructor === Date)

You can see the output results

Summarize

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