There are 8 data types for javascript
Value Type
- Number
- Null
- Undefined
- String
- Symbol
- Boolean
- BigInt
Reference Type
- Object
- Array
- Function
There are four ways to judge the data type
The first method: typeof
typeof null ---> "object"
typeof undefined ---> "undefined"
typeof true | false ---> 'boolean'
typeof 42 ---> 'number'
typeof "42" ---> 'string'
typeof { name : '1'} | [] ---> 'object'
typeof Symbol ---> 'symbol'
typeof ()=>{} ---> 'function'
typeof void 0 ---> 'undefined'The second method instanceof But this method is only suitable for judging object types
The instanceof operator is used to determine whether the object pointed to by the prototype attribute of a constructor exists on another prototype chain to detect the object.
For detailed introduction, please see here:instanceof operator in javascript
for example ： var arr = [] ; arr instanceof Array ---> true null instanceof Object ---> false [function] instanceof Object | Function --> true
The third method () This method can detect all data types, which is also the recommended method
Because toString is the prototype method of Object, Array Function and other examples are Object instances. All rewrite the toString method. Returns a string of type
(null) ---> [object Null]
(undefined) ---> [object Undefined]
(123) ---> [object Number]
(true) ---> [object Boolean]
('123') ---> [object String]
({}) ---> [object Object]
([]) ---> [object Array]
(Math) ---> [object Math]
(function(){}) ---> [object Function]
(new Date) ---> [object Date]
(Symbol()) ---> [object Symbol]The fourth method: constructor: The constructor that determines the object's constructor.
1. null yesjs The starting point of the prototype chain，No constructor 2. undefined No constructor 3. [].constructor === Array ---> true 4. [string].constructor === String 5. [object].constructor === object 6. [number].constructor === Number 7. [symbol].constructor === Symbol 8. [function].constructor === Function 9. [new Date].constructor === Date 10. [RegExp].constructor === RegExp
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