Common methods of JavaScript arrays for front-end developers

1. Modify the array

• array.pop
  removes the last element of the array.

var arr = [1, 2, 3];
arr.pop();// 返回 3
arr;// [1,2]

• array.shift
  removes the first element of the array

var arr = [1, 2, 3];
arr.shift();// 返回 1
arr;// [2,3]

• array.push
  adds one or more elements to the end of the array.

var arr = [];arr.push(1);// 返回数组长度 1
arr;// [1]
arr.push(2,3);
arr;// [1,2,3]

• array.unshift
  adds one or more elements to the beginning of the array.

var arr = [1, 2, 3];
arr.unshift(0);
arr.unshift(-3, -4);
arr;// [-3, -4, 0, 1, 2]

• array.reverse reverses
  the order of array elements.

var arr = [1, 2, 3];
arr.reverse();// [3, 2, 1]
arr;// [3, 2, 1]

• array.sort sorts
  an array.

var arr = [1 ,-1, 2];
arr.sort();// [-1, 1, 2]
arr;// [-1, 1, 2]
arr = [{age: 10,},{age: 1}, {age: 12}];// 按照 age 从小到大排序
arr.sort(function(a, b){return a.age - b.age > 0 ? 1 : -1;});

• array.splice
  adds or removes elements to an array.

// splice(开始下标, 删除个数，插入元素(可以多个)）var arr = [1, 2, 3, 4];
arr.splice(1, 2);// [2,3]
arr;// [1,4]
arr = [1, 2, 3, 4];
arr.splice(1, 1,'A','B','C');// [2,3]
arr;// [1, 2,"A","B","C", 4]

Note: When the array executes the above methods, the original array will be modified.

2. Iterative method

• array.forEach
  iterates over the array.

['a' ,'b' ,'c'].forEach(function(each, index){console.log(each,index);});
// 输出 'a' 0  'b' 1 'c' 2

• array.filter
  finds all elements from the array that match the specified criteria.

// 找出所有正数
var res = [3, 4, -1].filter(function(each){return each > 0;});
res; //[3,4]

• array.every
  Whether each element in the array satisfies the specified condition.

// 是否都为正数
var isAllPositive = [3, 4, -1].every(function(each){return each > 0;});
isAllPositive; // false;
isAllPositive = [3, 4].every(function(each){return each > 0;});
isAllPositive; // true;

• Whether any elements in the array.some
  array satisfy the specified condition.

// 是否有正数
var isSomePositive = [3, 4, -1].some(function(each){return each > 0;});
isSomePositive; // true;
isSomePositive = [-3, -4].every(function(each){return each > 0;});
isSomePositive; // false;

• array.map
  maps an array into another array.

// 内容 * 2[1, 2, 3].map(function(each){return each * 2;});
// 返回 [2, 4, 6]

• array.reduce
  combines an array into a single value.

// 数组内容求和。0 为初始值[1, 2, 3].reduce(function(prev, each){return prev + each;}, 0);// 返回 6

When iterative methods are to be used, forEach should be the last consideration. The main reason is: forEach has the worst semantics compared to other iteration methods. See avoid forEach for a more detailed description.

3 Other methods

• Whether Array.isArray
  is an array. IE9+ supports this method.

Array.isArray(1); // false
Array.isArray({}); // false
Array.isArray([]); // true

• array.concat concatenates
  an array or concatenates the values ​​of an array.

[1,2,3].concat(4,5); // 输出 [1, 2, 3, 4, 5]

• array.join
  merges all elements of an array into a string.

[1,2,3].join(); // 输出 '1,2,3'
[1,2,3].join('.'); // 输出 '1.2.3'

• array.slice
  selects a subset of elements in an array.

// slice(开始下标, 结束下标（可选，默认为数组长度）)
['a', 'b', 'c', 'd'].slice(1);// ["b", "c", "d"]
['a', 'b', 'c', 'd'].slice(1, 2);// ["b"]
['a', 'b', 'c', 'd'].slice(1, 3);// ["b", "c"]

• array.indexOf
  finds the index of the specified element in the array.

['a', 'b', 'c', 'd'].indexOf('c'); // 2
['a', 'b', 'c', 'd'].indexOf('g'); // -1

• array.lastIndexOf
  finds the index of the specified element in the array. The search direction is from back to front.

['c', 'd', 'c'].lastIndexOf('c'); // 2
['a', 'b', 'c', 'd'].lastIndexOf('g'); // -1