8個有用的JS技巧

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爲了保證的可讀性，本文采用意譯而非直譯。

這些技巧可能你們大部分都用過了，若是用過就看成加深點映像，若是沒有遇到過，就看成學會了幾個技巧。

1. 確保數組值

使用 grid ，須要從新建立原始數據，而且每行的列長度可能不匹配， 爲了確保不匹配行之間的長度相等，可使用Array.fill方法。

let array = Array(5).fill('');
console.log(array); // outputs (5) ["", "", "", "", ""]

2. 獲取數組惟一值

ES6 提供了從數組中提取唯一值的兩種很是簡潔的方法。不幸的是，它們不能很好地處理非基本類型的數組。在本文中，主要關注基本數據類型。

const cars = [
    'Mazda', 
    'Ford', 
    'Renault', 
    'Opel', 
    'Mazda'
]
const uniqueWithArrayFrom = Array.from(new Set(cars));
console.log(uniqueWithArrayFrom); // outputs ["Mazda", "Ford", "Renault", "Opel"]

const uniqueWithSpreadOperator = [...new Set(cars)];
console.log(uniqueWithSpreadOperator);// outputs ["Mazda", "Ford", "Renault", "Opel"]

3.使用展開運算符合並對象和對象數組

對象合併是很常見的事情，咱們可使用新的ES6特性來更好，更簡潔的處理合並的過程。

// merging objects
const product = { name: 'Milk', packaging: 'Plastic', price: '5$' }
const manufacturer = { name: 'Company Name', address: 'The Company Address' }

const productManufacturer = { ...product, ...manufacturer };
console.log(productManufacturer); 
// outputs { name: "Company Name", packaging: "Plastic", price: "5$", address: "The Company Address" }

// merging an array of objects into one
const cities = [
    { name: 'Paris', visited: 'no' },
    { name: 'Lyon', visited: 'no' },
    { name: 'Marseille', visited: 'yes' },
    { name: 'Rome', visited: 'yes' },
    { name: 'Milan', visited: 'no' },
    { name: 'Palermo', visited: 'yes' },
    { name: 'Genoa', visited: 'yes' },
    { name: 'Berlin', visited: 'no' },
    { name: 'Hamburg', visited: 'yes' },
    { name: 'New York', visited: 'yes' }
];

const result = cities.reduce((accumulator, item) => {
  return {
    ...accumulator,
    [item.name]: item.visited
  }
}, {});

console.log(result);
/* outputs
Berlin: "no"
Genoa: "yes"
Hamburg: "yes"
Lyon: "no"
Marseille: "yes"
Milan: "no"
New York: "yes"
Palermo: "yes"
Paris: "no"
Rome: "yes"
*/

4. 數組 map 的方法 (不使用Array.Map)

另外一種數組 map 的實現的方式，不用 Array.map。

Array.from 還能夠接受第二個參數，做用相似於數組的map方法，用來對每一個元素進行處理，將處理後的值放入返回的數組。以下：

const cities = [
    { name: 'Paris', visited: 'no' },
    { name: 'Lyon', visited: 'no' },
    { name: 'Marseille', visited: 'yes' },
    { name: 'Rome', visited: 'yes' },
    { name: 'Milan', visited: 'no' },
    { name: 'Palermo', visited: 'yes' },
    { name: 'Genoa', visited: 'yes' },
    { name: 'Berlin', visited: 'no' },
    { name: 'Hamburg', visited: 'yes' },
    { name: 'New York', visited: 'yes' }
];

const cityNames = Array.from(cities, ({ name}) => name);
console.log(cityNames);
// outputs ["Paris", "Lyon", "Marseille", "Rome", "Milan", "Palermo", "Genoa", "Berlin", "Hamburg", "New York"]

5. 有條件的對象屬性

再也不須要根據一個條件建立兩個不一樣的對象，可使用展開運算符號來處理。

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" }

6. 解構原始數據

有時候一個對象包含不少屬性，而咱們只須要其中的幾個，這裏可使用解構方式來提取咱們須要的屬性。如一個用戶對象內容以下：

const rawUser = {
   name: 'John',
   surname: 'Doe',
   email: 'john@doe.com',
   displayName: 'SuperCoolJohn',
   joined: '2016-05-05',
   image: 'path-to-the-image',
   followers: 45
   ...
}

咱們須要提取出兩個部分，分別是用戶及用戶信息，這時能夠這樣作:

let user = {}, userDetails = {};
({ name: user.name, surname: user.surname, ...userDetails } = rawUser);

console.log(user); // outputs { name: "John", surname: "Doe" }
console.log(userDetails); // outputs { email: "john@doe.com", displayName: "SuperCoolJohn", joined: "2016-05-05", image: "path-to-the-image", followers: 45 }

7. 動態屬性名

早期，若是屬性名須要是動態的，咱們首先必須聲明一個對象，而後分配一個屬性。這些日子已通過去了，有了ES6特性，咱們能夠作到這一點。

const dynamic = 'email';
let user = {
    name: 'John',
    [dynamic]: 'john@doe.com'
}
console.log(user); // outputs { name: "John", email: "john@doe.com" }

8.字符串插值

在用例中，若是正在構建一個基於模板的helper組件，那麼這一點就會很是突出，它使動態模板鏈接容易得多。

const user = {
  name: 'John',
  surname: 'Doe',
  details: {
    email: 'john@doe.com',
    displayName: 'SuperCoolJohn',
    joined: '2016-05-05',
    image: 'path-to-the-image',
    followers: 45
  }
}

const printUserInfo = (user) => { 
  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.`
  console.log(text);
}

printUserInfo(user);
// outputs 'The user is John Doe. Email: john@doe.com. Display Name: SuperCoolJohn. John has 45 followers.'

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