191 lines
4.9 KiB
Markdown
191 lines
4.9 KiB
Markdown
---
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title: Object Destructuring
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localeTitle: 对象解构
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---
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# 对象解构
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解构是从存储在对象中的数据中提取多个值的便捷方式。它可以在接收数据的位置使用(例如,分配的左侧)。 `ECMAScript 6`引入了此功能。
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如何提取值通过模式指定(请参阅示例)。
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### 基本任务
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```
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var userInfo = {name: 'neel', age: 22};
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var {name, age} = userInfo;
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console.log(name); // neel
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console.log(age); // 22
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```
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### 没有声明的作业
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变量可以通过与其声明分开的解构来赋值。
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```
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var name, age;
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({name, age} = {name: 'neel', age: 22});
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```
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> 在没有声明的情况下使用对象文字解构赋值时,赋值语句周围的`( .. )`是必需的语法。
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>
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> `{name, age} = {name: 'neel', age: 22}`不是有效的独立语法,因为左侧的`{name, age}`被视为块而不是对象文字。
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>
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> 但是, `({name, age} = {name: 'neel', age: 22})`是有效的,因为`var {name, age} = {name: 'neel', age: 22}`
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### 分配给新变量名称
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可以从对象解压缩属性,并将其分配给名称与对象属性不同的变量。
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```
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var userInfo = {a: 'neel', b: 22};
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var {a: name, b: bar} = userInfo;
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console.log(name); // neel
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console.log(bar); // 22
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```
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### 默认值
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如果`undefined`从对象解压缩的值,则可以为变量分配默认值。
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```
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var {name = 'ananonumys', age = 20} = {name: 'neel'};
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console.log(name); // neel
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console.log(age); // 20
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```
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### 分配新变量名称并提供默认值
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房产可以是两者
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1. 从对象解压缩并分配给具有不同名称的变量
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2. 如果unpacked值`undefined`分配一个默认值。
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```
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var {a:name = 'ananonumys', b:age = 20} = {age: 22};
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console.log(name); // ananonumys
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console.log(age); // 22
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```
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### 设置函数参数的默认值
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#### ES5版本
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```
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function getUserInfo(data) {
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data = data === undefined ? {} : data;
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var name = data.name === undefined ? 'ananonumys' : data.name;
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var age = data.age === undefined ? 20 : data.age;
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var location = data.location === undefined ? 'india' : data.location;
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console.log(name, age, location);
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// print user data
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}
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getUserInfo({
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name: 'neel',
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age: 22,
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location: 'canada'
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});
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```
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#### ES2015版本
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```
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function getUserInfo({name = 'ananonumys', age = 20, location = 'india'} = {}) {
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console.log(name, age, location);
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// print user data
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}
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getUserInfo({
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name: 'neel',
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age: 22,
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location: 'canada'
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});
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```
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> 在上面的`getUserInfo`的函数签名中,解构的左侧被分配给右侧的空对象文字: `{name = 'ananonumys', age = 20, location = 'india'} = {}` 。您也可以在没有右侧分配的情况下编写该函数。但是,如果省略右侧赋值,函数将在调用时查找至少一个要提供的参数,而在当前形式中,您只需调用`getUserInfo()`而不提供任何参数。如果您希望能够在不提供任何参数的情况下调用函数,则当前设计非常有用,另一个在您希望确保将对象传递给函数时非常有用。
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### 嵌套对象和数组解构
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```
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var metadata = {
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title: 'Scratchpad',
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translations: [
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{
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locale: 'de',
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localization_tags: [],
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last_edit: '2014-04-14T08:43:37',
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url: '/de/docs/Tools/Scratchpad',
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title: 'JavaScript-Umgebung'
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}
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],
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url: '/en-US/docs/Tools/Scratchpad'
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};
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var {title: englishTitle, translations: [{title: localeTitle}]} = metadata;
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console.log(englishTitle); // "Scratchpad"
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console.log(localeTitle); // "JavaScript-Umgebung"
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```
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### 用于迭代和解构
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```
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var people = [
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{
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name: 'Mike Smith',
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family: {
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mother: 'Jane Smith',
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father: 'Harry Smith',
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sister: 'Samantha Smith'
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},
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age: 35
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},
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{
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name: 'Tom Jones',
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family: {
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mother: 'Norah Jones',
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father: 'Richard Jones',
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brother: 'Howard Jones'
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},
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age: 25
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}
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];
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for (var {name: n, family: {father: f}} of people) {
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console.log('Name: ' + n + ', Father: ' + f);
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}
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// "Name: Mike Smith, Father: Harry Smith"
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// "Name: Tom Jones, Father: Richard Jones"
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```
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### 从作为函数参数传递的对象中解压缩字段
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```
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function userId({id}) {
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return id;
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}
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function whois({displayName, fullName: {firstName: name}}) {
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console.log(displayName + ' is ' + name);
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}
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var user = {
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id: 42,
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displayName: 'jdoe',
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fullName: {
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firstName: 'John',
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lastName: 'Doe'
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}
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};
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console.log('userId: ' + userId(user)); // "userId: 42"
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whois(user); // "jdoe is John"
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```
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这将解压缩用户对象中的`id` , `displayName`和`firstName`并打印它们。
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### 计算对象属性名称和解构
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```
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let key = 'z';
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let {[key]: foo} = {z: 'bar'};
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console.log(foo); // "bar"
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```
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另请参见: **对象解构** | [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment#Object_destructuring) |