javascript中类型检测的使用

javascript中类型检测的使用

1:typeof

使用：

typeof xxx

typeof 100 //"number"
typeof NaN //"number"
typeof "str"//"string"
typeof true //"boolean"
typeof function //"function"
typeof new Object()//"object"
typeof [1,2] //"object"
typeof null //"object"
typeof undefined //"undefined"

2:instanceof

使用：

obj instanceof Object

[1,2] instanceof Array //true
new Object() instanceof Array //false

example:

输入：

function Person(){}
function Student(){}

Student.prototype = new Person()
Student.prototype.constructor = Student

var person = new Student()
person instanceof Student // true
person instanceof Person // true

var student = new Person()
student instanceof Student // false
student instanceof Person // true

注意：

不同ifream与widnow之间的对象不能使用instanceof检测

3：Object.prototype.toString

Object.prototype.toString.apply([]) === "[object Array]" //true
Object.prototype.toString.apply(function(){}) === "[object Function]" //true
Object.prototype.toString.apply(null) === "[object Null]" // true
Object.prototype.toString.apply(undefined) === "[object Undefined]"//true

ie6,7,8

Object.prototype.toString.apply(null) === "[object Object]" // true

4: constructor

var num = 5
num.constructor == Number //true
"hello".constructor == String //true
true.constructor == Boolean //true
[1,2].constructor == Array //true
function person(){}
person.constructor == Function //true
var person = {}
person.constructor == Object //true
var person = new Person()
person.constructor == Person //true

5: duce type

根据各种数据类型自己的特点判断