JavaScript typeof
- Picha ya tatu Mapya ya JS
- Picha ya nne Mpangilio wa tafsiri ya JS
JavaScript typeof
在 JavaScript 中有 5 种不同的可以包含值的数据类型:
string
number
boolean
object
function
有 6 种类型的对象:
Object
Date
Array
String
Number
Boolean
以及 2 种不能包含值的数据类型:
null
undefined
typeof 运算符
您可以使用 typeof
运算符来确定 JavaScript 变量的数据类型。
Mifano
typeof "Bill" // 返回 "string" typeof 3.14 // 返回 "number" typeof NaN // 返回 "number" typeof false // 返回 "boolean" typeof [1,2,3,4] // 返回 "object" typeof {name:'Bill', age:19} // 返回 "object" typeof new Date() // 返回 "object" typeof function () {} // 返回 "function" typeof myCar // 返回 "undefined" * typeof null // 返回 "object"
请注意:
- NaN 的数据类型是数字
- 数组的数据类型是对象
- 日期的数据类型是对象
- null 的数据类型是 object
- 未定义变量的数据类型为 undefined *
- 未赋值的变量的数据类型也是 undefined *
您无法使用 typeof
来确定 JavaScript 对象是否是数组(或日期)。
原始日期
原始数据值指的是没有附加属性和方法的单个简单数据值。
typeof
运算符可以返回以下原始类型之一:
string
number
boolean
undefined
Mifano
typeof "Bill" // Inaisha "string" typeof 3.14 // Inaisha "number" typeof true // Inaisha "boolean" typeof false // Inaisha "boolean" typeof x // Inaisha "undefined" (if x has no value)
Data ya uadilifu
typeof
Operator inaisha aina mbinu ya data moja kati ya mabinafsi:
function
object
typeof
Operator inaisha viumbe, vijificho na null kwa "object".
typeof
Operator hauwezi kumwambia function "object".
Mifano
typeof {name:'Bill', age:19} // Inaisha "object" typeof [1,2,3,4] // Inaisha "object" (hakuna "array", angalia maelezo ya hapa chini) typeof null // Inaisha "object" typeof function myFunc(){} // Inaisha "function"
typeof
Operator inaisha viumbe kwa vijificho "object"
kwa sababu katika JavaScript, vijificho ni viumbe.
Data type ya operator typeof
typeof
Operator hauwezi kumwambia data type. Hauwezi kumwambia data type. Bado ni operator. Operator (+ - * /) hauwezi kumwambia data type.
lakini,typeof
Operator zaidi kufikiaInaisha stringi(kuna aina ya matokeo)。
Mashirika ya constructor
constructor
Mashirika ya properti inaishia kila matokeo wa JavaScript kwa mchakato wa kumaliza.
Mifano
"Bill".constructor // Inaisha function String() {[kampi cha kifupi]} (3.14).constructor // Inaisha function Number() {[kampi cha kifupi]} false.constructor // Inaisha function Boolean() {[kampi cha kifupi]} [1,2,3,4].constructor // Inaonekana function Array() {[native code]} {name:'Bill',age:19}.constructor // Inaonekana function Object() {[native code]} new Date().constructor // Inaonekana function Date() {[native code]} function () {}.constructor // Inaonekana function Function(){[native code]}
Unaweza kuangalia mabaki ya 'constructor' ili kubadilisha kwamba kina ni mafanikio (kumekadiri): "Array"
Kwa (ingawa):
Mifano
function isArray(myArray) { return myArray.constructor.toString().indexOf("Array") > -1; }
au bora zaidi, unaweza kuangalia kwamba kina niFaa leo kipya ya mafanikio:
Mifano
function isArray(myArray) { return myArray.constructor === Array; }
Unaweza kuangalia mabaki ya 'constructor' ili kubadilisha kwamba kina ni tarehe (kumekadiri): "Date"
Kwa (ingawa):
Mifano
function isDate(myDate) { return myDate.constructor.toString().indexOf("Date") > -1; }
au bora zaidi, unaweza kuangalia kwamba kina niFaa leo kipya:
Mifano
function isDate(myDate) { return myDate.constructor === Date; }
Bila yaangalau
Kwenye JavaScript, muona yana wakati bila wakati yake ni undefined
. Aina pia itakuwa undefined
.
Mifano
let car; // Wakati ni undefined, aina pia ni undefined.
Kwa kumaliza wakati wake kwa undefined
inaweza kumaliza kila muona. Aina pia itakuwa undefined
.
Mifano
car = undefined; // Wakati ni undefined, aina pia ni undefined.
Bila yaangalau
Bila yaangalau na, undefined
Haukumia.
Bila yaangalau niwe niwe niwe, ina wakati na aina.
Mifano
let car = ""; // Wakati ni "", aina ni 'string'
Bila
Kwenye JavaScript, null
inaangalia 'bila' yaani 'bila'. Niwe niwe niwe yanaonekana.
Mafaragati, kwenye JavaScript,null
数据类型 niwe niwe niwe.
Inaweza kusema kwamba hii ni kosa cha JavaScript kwa kuzalishwa.typeof null
Ni mifano ya kuzalishwa. Aina inayotarajiwa ni null
.
Inaweza kumekota kwa kusoma kwa kufikia null
Tenda kwa kumekota kwa kusoma kila mifano:
Mifano
let person = {firstName:"Bill", lastName:"Gates", age:19, eyeColor:"blue"}; person = null; // Hivi sasa thamani ni null, lakini aina inaendelea kuwa object
Inaweza kumekota kwa kusoma kwa kufikia undefined
Tenda kwa kumekota kwa kusoma kila mifano:
Mifano
let person = {firstName:"Bill", lastName:"Gates", age:19, eyeColor:"blue"}; person = undefined; // Hivi sasa, thamani na aina zinafuata
Muundo wa undefined na null
undefined
na null
Wazito wana ukweli lakini aina tumewahitisha:
typeof undefined // undefined typeof null // object null === undefined // false null == undefined // true
- Picha ya tatu Mapya ya JS
- Picha ya nne Mpangilio wa tafsiri ya JS