8个有用的JavaScript技巧

英文原文: https://devinduct.com/blogpost/26/8-useful-javascript-tricks

介绍

每种编程语言都有其独特的技巧。他们中的许多人是开发人员所熟知的,但是其中一些却有些骇人听闻。在本文中,我将向您展示一些我认为有用的技巧。我在实践中使用过的其中一些是解决旧问题的新方法。请享用!

1.确保数组值

曾经在需要重新创建原始数据的网格中工作过吗?嗯,我有!为了确保不匹配的行之间的长度相等,可以使用Array。填充方法。

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

2.获取数组唯一值

ES6提供了两种非常巧妙的方法来从数组中提取唯一值。不幸的是,它们不能很好地填充非基本类型的数组。您可以稍后在此链接上阅读有关此内容的更多信息。处理数组重复可能很棘手。在本文中,我们将重点介绍原始数据类型。

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.使用传播运算符合并对象和对象数组

对象合并并不是一件难事,过去您很有可能做到了,将来也有可能做到。不同之处在于,过去您是手动完成大部分工作的,但是现在和将来,您将使用新的ES6功能。

// 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);

Berlin: "no"
Genoa: "yes"
Hamburg: "yes"
Lyon: "no"
Marseille: "yes"
Milan: "no"
New York: "yes"
Palermo: "yes"
Paris: "no"
Rome: "yes"

4.映射数组(不带Array.map)

您是否知道还有另一种不包含方法的映射数组值的Array.map方法?如果没有,请在下面检查。

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.条件对象属性

不再需要根据条件创建两个不同的对象以使其具有特定的属性。为此,散布算子非常适合。

const getUser = (emailIncluded) => {
  return {
    name: 'John',
    surname: 'Doe',
    ...emailIncluded && { email : 'john@doe.com' }
    // or, if the && operator pattern is hard to read use ternary operator
    // ...emailIncluded ? { email : 'john@doe.com' } : null
  }
}

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.破坏原始数据

您是否曾经处理过包含太多数据的对象?我很确定你有。可能最常见的情况是,当我们有一个包含整体数据以及详细信息的用户对象时。在这里,我们可以将新的ES破坏功能称为救援。让我们用一个示例对此进行备份。

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

可以通过拆分为两个对象,以更上下文相关的方式表示上面的对象,如下所示:

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.动态属性名称

在过去,我们首先必须声明一个对象,然后如果该属性名称需要动态,则分配一个属性。这不可能以声明的方式实现。这些天已经过去,有了ES6功能,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

最后但并非最不重要的是串联字符串的新方法。可以真正发挥作用的用例是,如果您正在构建基于模板的帮助器组件。它使动态模板串联变得容易得多。

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.'

结论

JavaScript世界正在迅速扩展。这里有很多很酷的功能,随时可以使用。棘手且耗时的问题已逐渐淡出过去,并且借助ES6的新功能,可立即使用解决方案。

英文原文: https://devinduct.com/blogpost/26/8-useful-javascript-tricks

李, 国轩