JS 数组常用的方法总结(不断补充中。。。)

1 删除数组的重复项

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

// First method
var uniqueFruits = Array.from(new Set(fruits));
console.log(uniqueFruits); // returns [“banana”, “apple”, “orange”, “watermelon”, “grape”]
// Second method
var uniqueFruits2 = […new Set(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，有一种很好的简短方法可以做到这一点，咱们可以使用.splice(start、value to remove、valueToAdd)，这些参数指定咱们希望从哪里开始修改、修改多少个值和替换新值。

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 Array.from 达到 .map 的效果

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.置空数组

有时候我们需要清空数组，一个快捷的方法就是直接让数组的 length 属性为 0，就可以清空数组了。

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

有时候，出于某种目的，需要将数组转化成对象，一个简单快速的方法是就使用展开运算符号(...):

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

在某些情况下，当咱们创建一个数组并希望用一些数据来填充它，这时 .fill()方法可以帮助咱们。

var newArray = new Array(10).fill(“1”);
console.log(newArray); // returns [“1”, “1”, “1”, “1”, “1”, “1”, “1”, “1”, “1”, “1”, “1”]

7 数组合并

使用展开操作符，也可以将多个数组合并起来。 

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

求两个数组的交集在面试中也是有一定难度的正点，为了找到两个数组的交集，首先使用上面的方法确保所检查数组中的值不重复，接着使用.filter 方法和.includes方法。如下所示： 

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

9.从数组中删除虚值

在 JS 中，虚值有 false, 0，''， null, NaN, undefined。咱们可以 .filter() 方法来过滤这些虚值。

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

10 从数组中获取随机值

有时我们需要从数组中随机选择一个值。一种方便的方法是可以根据数组长度获得一个随机索引，如下所示：

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

11.反转数组
现在，咱们需要反转数组时，没有必要通过复杂的循环和函数来创建它，数组的 reverse 方法就可以做了：

ar 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
某个元素在数组中最后出现的位置的下标：

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.对数组中的所有值求和
JS 面试中也经常用 reduce 方法来巧妙的解决问题

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