JavaScript data types
- string: string
- number: number
- boolean: Boolean value
- undefined: undefined
- null: empty value
- object: object (including arrays and functions)
- symbol: symbol, unique value (ES6 new)
1. Defects of typeof
typeofYou can judge the types of string, number, boolean, undefined, symbol, functionetc., but not the type nullof object.
var str = "Hello";
var num = 123;
var bool = true;
var undf;
var nl = null;
var obj = {
name: "John", age: 25};
var arr = [1, 2, 3];
var func = function() {
};
var sym = Symbol("mySymbol");
console.log(typeof str); // 输出：string
console.log(typeof num); // 输出：number
console.log(typeof bool); // 输出：boolean
console.log(typeof undf); // 输出：undefined
console.log(typeof nl); // 输出：object
console.log(typeof obj); // 输出：object
console.log(typeof arr); // 输出：object
console.log(typeof func); // 输出：function
console.log(typeof sym); // 输出：symbol
Note: typeofCannot distinguish null, Object, Array. typeof judges that all three types return 'object'.
2. Determine whether it is an array
method 1
Use instanceofto determine whether the data is an array.
[] instanceof Array // true
It should be noted that instanceofit cannot be used to judge whether it is an object type, because an array is also an object.
[] instanceof Object // true
{
} instanceof Object // true
Method 2
The constructor can also determine whether it is an array.
[].constructor === Array // true
Method 3
Object.prototype.toString.call()Various types of objects can be obtained.
Object.prototype.toString.call([]) === '[object Array]' // true
Object.prototype.toString.call({
}) === '[object Object]' // true
This method can also be used to determine whether it is a promise object.
let obj = new Promise()
Object.prototype.toString.call(obj) === '[object Promise]' // true
Method 4
Use the array's isArray() method to judge.
Array.isArray([]) // true
Method 5
Object.getPrototypeOf(val) === Array.prototype // true
3. Judging whether it is an object
Method 1 (recommended)
Object.prototype.toString.call() Various types of objects can be obtained.
Object.prototype.toString.call({
}) === '[object Object]' // true
Method 2
Object.getPrototypeOf(val) === Object.prototype // true