摘要：不幸的是，它們不能很好地處理非基本類型的數(shù)組。還可以接受第二個參數(shù)，作用類似于數(shù)組的方法，用來對每個元素進行處理，將處理后的值放入返回的數(shù)組。

為了保證的可讀性，本文采用意譯而非直譯。

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這些技巧可能大家大部分都用過了，如果用過就當(dāng)作加深點映像，如果沒有遇到過，就當(dāng)作學(xué)會了幾個技巧。

使用 grid ，需要重新創(chuàng)建原始數(shù)據(jù)，并且每行的列長度可能不匹配， 為了確保不匹配行之間的長度相等，可以使用Array.fill方法。

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

ES6 提供了從數(shù)組中提取惟一值的兩種非常簡潔的方法。不幸的是，它們不能很好地處理非基本類型的數(shù)組。在本文中，主要關(guān)注基本數(shù)據(jù)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"]

對象合并是很常見的事情，我們可以使用新的ES6特性來更好，更簡潔的處理合并的過程。

// 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"
*/

另一種數(shù)組 map 的實現(xiàn)的方式，不用 Array.map。

Array.from 還可以接受第二個參數(shù)，作用類似于數(shù)組的map方法，用來對每個元素進行處理，將處理后的值放入返回的數(shù)組。如下：

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"]

不再需要根據(jù)一個條件創(chuàng)建兩個不同的對象，可以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" }

有時候一個對象包含很多屬性，而我們只需要其中的幾個，這里可以使用解構(gòu)方式來提取我們需要的屬性。如一個用戶對象內(nèi)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
   ...
}

我們需要提取出兩個部分，分別是用戶及用戶信息，這時可以這樣做:

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 }

早期，如果屬性名需要是動態(tài)的，我們首先必須聲明一個對象，然后分配一個屬性。這些日子已經(jīng)過去了，有了ES6特性，我們可以做到這一點。

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

在用例中，如果正在構(gòu)建一個基于模板的helper組件，那么這一點就會非常突出，它使動態(tài)模板連接容易得多。

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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