标签：类型 不能 对象属性 red 基本数据类型 基本 条件 创建 关注
使用 grid ，需要重新创建原始数据，并且每行的列长度可能不匹配， 为了确保不匹配行之间的长度相等，可以使用Array.fill方法。
let array = Array(5).fill(‘‘); console.log(array); // outputs (5) ["", "", "", "", ""]
ES6 提供了从数组中提取惟一值的两种非常简洁的方法。不幸的是，它们不能很好地处理非基本类型的数组。在本文中，主要关注基本数据类型。
1 const cars = [ 2 ‘Mazda‘, 3 ‘Ford‘, 4 ‘Renault‘, 5 ‘Opel‘, 6 ‘Mazda‘ 7 ] 8 const uniqueWithArrayFrom = Array.from(new Set(cars)); 9 console.log(uniqueWithArrayFrom); // outputs ["Mazda", "Ford", "Renault", "Opel"] 10 11 const uniqueWithSpreadOperator = [...new Set(cars)]; 12 console.log(uniqueWithSpreadOperator);// outputs ["Mazda", "Ford", "Renault", "Opel"]
对象合并是很常见的事情，我们可以使用新的ES6特性来更好，更简洁的处理合并的过程。
1 // merging objects 2 const product = { name: ‘Milk‘, packaging: ‘Plastic‘, price: ‘5$‘ } 3 const manufacturer = { name: ‘Company Name‘, address: ‘The Company Address‘ } 4 5 const productManufacturer = { ...product, ...manufacturer }; 6 console.log(productManufacturer); 7 // outputs { name: "Company Name", packaging: "Plastic", price: "5$", address: "The Company Address" } 8 9 // merging an array of objects into one 10 const cities = [ 11 { name: ‘Paris‘, visited: ‘no‘ }, 12 { name: ‘Lyon‘, visited: ‘no‘ }, 13 { name: ‘Marseille‘, visited: ‘yes‘ }, 14 { name: ‘Rome‘, visited: ‘yes‘ }, 15 { name: ‘Milan‘, visited: ‘no‘ }, 16 { name: ‘Palermo‘, visited: ‘yes‘ }, 17 { name: ‘Genoa‘, visited: ‘yes‘ }, 18 { name: ‘Berlin‘, visited: ‘no‘ }, 19 { name: ‘Hamburg‘, visited: ‘yes‘ }, 20 { name: ‘New York‘, visited: ‘yes‘ } 21 ]; 22 23 const result = cities.reduce((accumulator, item) => { 24 return { 25 ...accumulator, 26 [item.name]: item.visited 27 } 28 }, {}); 29 30 console.log(result); 31 /* outputs 32 Berlin: "no" 33 Genoa: "yes" 34 Hamburg: "yes" 35 Lyon: "no" 36 Marseille: "yes" 37 Milan: "no" 38 New York: "yes" 39 Palermo: "yes" 40 Paris: "no" 41 Rome: "yes" 42 */
另一种数组 map 的实现的方式，不用 Array.map。
Array.from 还可以接受第二个参数，作用类似于数组的map方法，用来对每个元素进行处理，将处理后的值放入返回的数组。如下：
1 const cities = [ 2 { name: ‘Paris‘, visited: ‘no‘ }, 3 { name: ‘Lyon‘, visited: ‘no‘ }, 4 { name: ‘Marseille‘, visited: ‘yes‘ }, 5 { name: ‘Rome‘, visited: ‘yes‘ }, 6 { name: ‘Milan‘, visited: ‘no‘ }, 7 { name: ‘Palermo‘, visited: ‘yes‘ }, 8 { name: ‘Genoa‘, visited: ‘yes‘ }, 9 { name: ‘Berlin‘, visited: ‘no‘ }, 10 { name: ‘Hamburg‘, visited: ‘yes‘ }, 11 { name: ‘New York‘, visited: ‘yes‘ } 12 ]; 13 14 const cityNames = Array.from(cities, ({ name}) => name); 15 console.log(cityNames); 16 // outputs ["Paris", "Lyon", "Marseille", "Rome", "Milan", "Palermo", "Genoa", "Berlin", "Hamburg", "New York"]
不再需要根据一个条件创建两个不同的对象，可以使用展开运算符号来处理。
nst getUser = (emailIncluded) => { return { name: ‘John‘, surname: ‘Doe‘, ...emailIncluded && { email : ‘john@doe.com‘ } } } const user = getUser(true); console.log(user); // outputs { name: "John", surname: "Doe", email: "john@doe.com" } const userWithoutEmail = getUser(false); console.log(userWithoutEmail); // outputs { name: "John", surname: "Doe" }
有时候一个对象包含很多属性，而我们只需要其中的几个，这里可以使用解构方式来提取我们需要的属性。如一个用户对象内容如下：
const rawUser = { name: ‘John‘, surname: ‘Doe‘, email: ‘john@doe.com‘, displayName: ‘SuperCoolJohn‘, joined: ‘2016-05-05‘, image: ‘path-to-the-image‘, followers: 45 ... }
我们需要提取出两个部分，分别是用户及用户信息，这时可以这样做:
1 let user = {}, userDetails = {}; 2 ({ name: user.name, surname: user.surname, ...userDetails } = rawUser); 3 4 console.log(user); // outputs { name: "John", surname: "Doe" } 5 console.log(userDetails); // outputs { email: "john@doe.com", displayName: "SuperCoolJohn", joined: "2016-05-05", image: "path-to-the-image", followers: 45 }
早期，如果属性名需要是动态的，我们首先必须声明一个对象，然后分配一个属性。这些日子已经过去了，有了ES6特性，我们可以做到这一点。
1 const dynamic = ‘email‘; 2 let user = { 3 name: ‘John‘, 4 [dynamic]: ‘john@doe.com‘ 5 } 6 console.log(user); // outputs { name: "John", email: "john@doe.com" }
在用例中，如果正在构建一个基于模板的helper组件，那么这一点就会非常突出，它使动态模板连接容易得多。
1 const user = { 2 name: ‘John‘, 3 surname: ‘Doe‘, 4 details: { 5 email: ‘john@doe.com‘, 6 displayName: ‘SuperCoolJohn‘, 7 joined: ‘2016-05-05‘, 8 image: ‘path-to-the-image‘, 9 followers: 45 10 } 11 } 12 13 const printUserInfo = (user) => { 14 const text = `The user is ${user.name} ${user.surname}. Email: ${user.details.email}. Display Name: ${user.details.displayName}. ${user.name} has ${user.details.followers} followers.` 15 console.log(text); 16 } 17 18 printUserInfo(user); 19 // outputs ‘The user is John Doe. Email: john@doe.com. Display Name: SuperCoolJohn. John has 45 followers.‘
标签：类型 不能 对象属性 red 基本数据类型 基本 条件 创建 关注
原文地址：https://www.cnblogs.com/Object-L/p/12200775.html
