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8個有用的JS技巧

來源:前端小智 發布時間:2019-07-08 閱讀次數:

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

 1. 確保數組值

  使用 grid ,需要重新創建原始數據,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) ["", "", "", "", ""]

 2. 獲取數組唯一值

  ES6 提供了從數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.使用展開運算符合并對象和對象數組

  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"
*/

 4. 數組 map 的方法 (不使用Array.Map)

  另一種數組 map 的實現的方式,不用 Array.map。

  Array.from 還可以接受第二個參數,作用類似于數組的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"]

 5. 有條件的對象屬性

  不再需要根據一個條件創建兩個不同的對象,可以使用展開運算符號來處理。

nst getUser = (emailIncluded) => {
  return {
    name: 'John',
    surname: 'Doe',
    ...emailIncluded && { email : '[email protected]' }
  }
}

const user = getUser(true);
console.log(user); // outputs { name: "John", surname: "Doe", email: "[email protected]" }

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很多屬性,而我們只需要其中的幾個,這里可以使用解構方式來提取我們需要的屬性。如一個用戶對象內容如下:

const rawUser = {
   name: 'John',
   surname: 'Doe',
   email: '[email protected]',
   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: "[email protected]", displayName: "SuperCoolJohn", joined: "2016-05-05", image: "path-to-the-image", followers: 45 }

 7. 動態屬性名

  早期,如果屬性名需要是動態的,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]: '[email protected]'
}
console.log(user); // outputs { name: "John", email: "[email protected]" }

 8.字符串插值

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

const user = {
  name: 'John',
  surname: 'Doe',
  details: {
    email: '[email protected]',
    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: [email protected] Display Name: SuperCoolJohn. John has 45 followers.'

  原文鏈接:https://devinduct.com/blogpost/26/8-useful-javascript-tricks

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