工作中遇到的数组技巧

来自公众号：前端Q

原文：https://www.blog.duomly.com/13-useful-javascript-array-tips-and-tricks-you-should-know/

1. 数组去重

var fruits = ["banana", "apple", "orange", "watermelon", "apple", "orange", "grape", "apple"];
 
// First method
var uniqueFruits = Array.from(newSet(fruits));
console.log(uniqueFruits);
// returns ["banana", "apple", "orange", "watermelon", "grape"]

// Second method
var uniqueFruits2 = […newSet(fruits)];
console.log(uniqueFruits2);
// returns ["banana", "apple", "orange", "watermelon", "grape"]

2. 替换数组中的特定值

有时在创建代码时需要替换数组中的特定值，有一种很好的简单的方法可以做到这一点，我们可以使用.splice(start、valueToRemove、valueToAdd)，并将所有三个参数传递给它，这些参数可以指定我们希望从哪里开始修改、希望修改多少值和新值。

var fruits = ["banana", "apple", "orange", "watermelon", "apple", "orange", "grape", "apple"];
fruits.splice(0, 2, "potato", "tomato");
console.log(fruits);
// returns ["potato", "tomato", "orange", "watermelon", "apple", "orange", "grape", "apple"]

3. 没有map()的映射数组

var friends = [
    { name: "John", age: 22 },
    { name: "Peter", age: 23 },
    { name: "Mark", age: 24 },
    { name: "Maria", age: 22 },
    { name: "Monica", age: 21 },
    { name: "Martha", age: 19 },
]
 

var friendsNames = Array.from(friends, ({name}) => name);
console.log(friendsNames);
// returns ["John", "Peter", "Mark", "Maria", "Monica", "Martha"]

4.空数组

var fruits = ["banana", "apple", "orange", "watermelon", "apple", "orange", "grape", "apple"];
 

fruits.length = 0;
console.log(fruits);
 // returns []

5.将数组转换为对象

var fruits = ["banana", "apple", "orange", "watermelon"];
var fruitsObj = { …fruits };
console.log(fruitsObj);
// returns {0: "banana", 1: "apple", 2: "orange", 3: "watermelon", 4: "apple", 5: "orange", 6: "grape", 7: "apple"}

6. 用数据填充数组

var newArray = newArray(10).fill("1");
console.log(newArray);
// returns ["1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "1"]

7. 合并数组

var fruits = ["apple", "banana", "orange"];
var meat = ["poultry", "beef", "fish"];
var vegetables = ["potato", "tomato", "cucumber"];
var food = […fruits, …meat, …vegetables];
console.log(food);
// ["apple", "banana", "orange", "poultry", "beef", "fish", "potato", "tomato", "cucumber"]

8. 求两个数组的交集

var numOne = [0, 2, 4, 6, 8, 8];
var numTwo = [1, 2, 3, 4, 5, 6];
var duplicatedValues = […newSet(numOne)].filter(item => numTwo.includes(item));
console.log(duplicatedValues);
// returns [2, 4, 6]

9. 从数组中删除假值

var mixedArr = [0, "blue", "", NaN, 9, true, undefined, "white", false];
var trueArr = mixedArr.filter(Boolean);
console.log(trueArr);
// returns ["blue", 9, true, "white"]

10. 从数组中获取随机值

var colors = ["blue", "white", "green", "navy", "pink", "purple", "orange", "yellow", "black", "brown"];
var randomColor = colors[(Math.floor(Math.random() * (colors.length  )))]

11. 数组反转

var colors = ["blue", "white", "green", "navy", "pink", "purple", "orange", "yellow", "black", "brown"];
var reversedColors = colors.reverse();
console.log(reversedColors);
// returns ["brown", "black", "yellow", "orange", "purple", "pink", "navy", "green", "white", "blue"]

12. .lastIndexOf()方法

在Javascript中，有一个有趣的方法，它允许查找给定元素的最后一次出现的索引。例如，如果我们的数组有重复的值，我们可以找到它最后一次出现的位置。让我们看看代码示例:

var nums = [1, 5, 2, 6, 3, 5, 2, 3, 6, 5, 2, 7];
var lastIndex = nums.lastIndexOf(5);
console.log(lastIndex);
// returns 9

13. 将数组中的所有值相加

var nums = [1, 5, 2, 6];
var sum = nums.reduce((x, y) => x + y);
console.log(sum);
// returns 14