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Summary of Boolean value types of different data in js: false: empty string; null; undefined; 0; NaN. true: Except for the above false case, everything else is true;
There are six data types in javascript: string;boolean;Array;Object;null;undefined. How to detect these data types, the summary method is as follows:
The first method: typeof
var obj = {'name':'Tom'} var arr = ['a','b','c'] var str = 'chenxinming' var bool = true var num = 1 var n = null var fn = function(n){ console.log(n) } console.log(typeof obj) // object console.log(typeof arr) // object console.log(typeof str) // string console.log(typeof bool) // boolean console.log(typeof num) // number console.log(typeof n) // object console.log(typeof fn) // function
Through the above test, it is found that typeof returns both types when detecting arrays and dictionaries. It is an Object, and it is impossible to tell whether it is an array or an object. If you want to check whether it is an array or an object, use the instanceof method and constructor method
Second method: instanceof
var obj = {'name':'Tom'} var arr = ['a','b','c'] var str = 'chenxinming' var bool = true var num = 1 var n = null var fn = function(n){ console.log(n) } console.log(obj instanceof Object) // true console.log(arr instanceof Array) // true console.log(str instanceof String) // false console.log(bool instanceof Boolean) // false console.log(num instanceof Number) // false console.log(n instanceof Object) // false console.log(fn instanceof Function) // true
Note: instanceof can only be used to determine arrays and objects , function cannot judge string, number and boolean types. If you need to judge string and boolean, you can use the tostring() method.
Special note:
The instanceof method returns True when checking whether the array is an object
var arr = ['a','b','c'] console.log(arr instanceof Object) // true
If you use instanceof, you need to strictly judge whether it is an array Or when it is an object, the improved code is as follows:
var obj = {'name':'Tom'} var arr = ['a','b','c'] var str = 'chenxinming' var getDataType = function(data){ if(data instanceof Array){ return 'Array' } else if (data instanceof Object){ return 'Object' } else{ return 'data is not obejct type' } } getDataType(obj) // Object getDataType(obj) // Array getDataType(obj) // data is not obejct type
The third method: constructor
var obj = {'name':'Tom'} var arr = ['a','b','c'] var str = 'chenxinming' var bool = true var num = 1 var n = null var fn = function(n){ console.log(n) } console.log(obj.constructor == Object) // true console.log(arr.constructor == Array) // true console.log(str.constructor == String) // true console.log(bool.constructor == Boolean) // true console.log(num.constructor == Number) // true console.log(fn.constructor == Function) // true
The test found that the constructor supports checking Object, Array, String, Boolean, Number, Function
The fourth method: toString (recommended)
var obj = {'name':'Tom'} var arr = ['a','b','c'] var str = 'chenxinming' var bool = true var num = 1 var n = null var fn = function(n){ console.log(n) } console.log(Object.prototype.toString.call(obj)) // [object Object] console.log(Object.prototype.toString.call(arr)) // [object Array] console.log(Object.prototype.toString.call(str)) // [object String] console.log(Object.prototype.toString.call(bool)) // [object Boolean] console.log(Object.prototype.toString.call(num)) // [object Number] console.log(Object.prototype.toString.call(n)) // [object Null] console.log(Object.prototype.toString.call(fn)) // [object Function]
From the test, it is best to use toString. This method has more comprehensive functions.
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