五个必须知道的 JavaScript 数组方法_js教程

介绍

五个必须知道的 JavaScript 数组方法

数组非常适合存储相关数据，并且通常用作组织信息的一种方式。我们中的大多数人每天都在使用它们，但是您知道 JavaScript 中还内置了一些非常简洁的数组方法吗？

这些方法使我们的生活变得更加轻松，将多行代码优化为一个简单的命令。无论您是刚开始使用数组还是已经感觉自己是专家，本文都将帮助您在使用它们时变得更有效率。

filter（）

如果您想根据特定条件过滤数组，您可能需要 filter() 方法。这是一个有用的函数，它将返回一个包含您感兴趣的所有项目的新数组。

它需要一个函数作为参数，它将为数组中的每个元素调用。如果函数返回 true，则该元素将保留在数组中；否则，它将从数组中删除。

例子

我们已从后端请求数据，并希望根据对象数组具有的属性进行客户端过滤。在这种情况下，我们已从 JokeAPI 请求笑话，并希望过滤类别属性等于 Programming 的笑话。

const response = { "error": false, "amount": 4, "jokes": [
        { "category": "Programming", "type": "single", "joke": "Judge: \"I sentence you to the maximum punishment...\"\nMe (thinking): \"Please be death, please be death...\"\nJudge: \"Learn Java!\"\nMe: \"Damn.\"", "id": 45, "safe": true, "lang": "en" },
        { "category": "Christmas", "type": "twopart", "setup": "How will Christmas dinner be different after Brexit?", "delivery": "No Brussels!", "id": 251, "safe": false, "lang": "en" },
        { "category": "Christmas", "type": "twopart", "setup": "What do Santa's little helpers learn at school?", "delivery": "The elf-abet!\n", "id": 248, "safe": true, "lang": "en" },
        { "category": "Christmas", "type": "twopart", "setup": "Why couldn't the skeleton go to the Christmas party?", "delivery": "Because he had no body to go with!", "id": 252, "safe": true, "lang": "en" }
    ]
} const programmingJokes = response.jokes.filter((joke) => joke.category === "Programming" ); console.log("programmingJokes: ", programmingJokes);

programmingJokes: [
  { "category": "Programming", "type": "single", "joke": "Judge: \"I sentence you to the maximum punishment...\"\nMe (thinking): \"Please be death, please be death...\"\nJudge: \"Learn Java!\"\nMe: \"Damn.\"", "id": 45, "safe": true, "lang": "en" },
]

map（）

map() 方法转换数组中的每一项，对其应用一个函数并将结果存储在一个新数组中，而不实际更改初始数组。

例子

我们已从后端请求数据，并希望从该数据中提取信息。在这种情况下，我们从 RandomDataAPI 请求随机用户数据，并希望将每个人的年龄提取到一个数组中。

const response = [
  { "id": 7433, "uid": "4c2c1731-2c3c-4983-b39f-0f988791e98f", "password": "L903JpXGAj", "first_name": "Dalene", "last_name": "Kuhn", "username": "dalene.kuhn", "email": "dalene.kuhn@email.com", "avatar": "https://robohash.org/autmagnisunt.png?size=300x300&set=set1", "gender": "Agender", "phone_number": "+964 771-857-9446 x77784", "social_insurance_number": "607847845", "age": 25,
  },
  { "id": 3764, "uid": "0c1c9485-2b90-4e68-a795-0e4925aa8344", "password": "XjyI92Y1dl", "first_name": "Laurence", "last_name": "Lowe", "username": "laurence.lowe", "email": "laurence.lowe@email.com", "avatar": "https://robohash.org/quinonomnis.png?size=300x300&set=set1", "gender": "Agender", "phone_number": "+689 743-128-5476 x530", "social_insurance_number": "737935460", "age": 30,
  },
  { "id": 9408, "uid": "4933cb5d-f4f5-4bc3-8d37-f4c9b3129923", "password": "JrI8e4KVjs", "first_name": "Gabriella", "last_name": "Tillman", "username": "gabriella.tillman", "email": "gabriella.tillman@email.com", "avatar": "https://robohash.org/repellatmaioresmolestiae.png?size=300x300&set=set1", "gender": "Bigender", "phone_number": "+675 552-834-4168 x39534", "age": 21,
  }
] const arrayOfAges = response.map(person person.age); console.log("arrayOfAges: ", arrayOfAges)

arrayOfAges: [25, 30, 21]

reduce（）

reduce() 方法通过对每个元素应用一个函数并累积结果，将数组缩减为单个值。这是查找总数或查找所有项目平均值的好方法。

例子

我们有一个包含每月存款的数组，我们想知道所有存款的总和。

const depositsArray = [{ id: 1231, deposit: 5, currency: '$',},{ id: 1231, deposit: 10, currency: '$',},{ id: 1231, deposit: 20, currency: '$',},{ id: 1231, deposit: 5, currency: '$',},{ id: 1231, deposit: 15, currency: '$',},
]; const sumOfDeposits = depositsArray.reduce((total, transaction) => total + transaction.deposit, 0 ); console.log('depositsArray: ', depositsArray); console.log('sumOfDeposits: ', sumOfDeposits);

depositsArray: [{...}, {...}, {...}, {...}, {...}] sumOfDeposits: 55

some（）

some() 方法检查数组中的至少一个元素是否满足由提供的函数实现的测试。如果它确实满足测试，它将返回true；否则，它将返回 false。

例子

我们已从后端请求用户，并想知道其中一个是否已被标记为机器人。

const response = [
  { id: 101, firstName: 'Muhammad', lastName: 'Ovi', age: 25, isBot: false,
  },
    { id: 102, firstName: 'John', lastName: 'Doe', age: 30, isBot: true,
  },
    { id: 103, firstName: 'Chris', lastName: 'Smith', age: 27, isBot: false,
  },
]; const isNotValidUsers = response.some((user) => user.isBot === false); console.log("isNotValidUsers: ", isNotValidUsers)

isNotValidUsers: true

every（）

every() 方法检查数组中的每个元素是否满足由提供的函数实现的测试。如果是，它将返回 true；否则，它将返回 false

例子

我们的购物车中有一份产品清单，想检查是否有库存。

const response = [
    { "id": 1, "title": "iPhone 9", "price": 549, "discountPercentage": 12.96, "rating": 4.69, "stock": 94 },
    { "id": 2, "title": "Apple Watch", "price": 300, "discountPercentage": 10, "rating": 4.40, "stock": 20 },
     { "id": 3, "title": "Apple Headphones", "price": 600, "discountPercentage": 7, "rating": 4.65, "stock": 2 },
] const hasStock = response.every((item) => item.stock > 0); console.log("hasStock: ", hasStock);