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8个有用的JS技巧

为了保证的可读性,本文采用意译而非直译。

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这些技巧可能大家大部分都用过了,如果用过就当作加深点映像,如果没有遇到过,就当作学会了几个技巧。

1. 确保数组值

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) ["","", "","", ""]

2. 获取数组唯一值

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。

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. 使用展开运算符合并对象和对象数组

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。

// 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. 数组 map 的方法 (不使用 Array.Map)

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:

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. 有条件的对象属性

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"}

6. 解构原始数据

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:

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. 动态属性名

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。

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,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。

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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