不改变原数组

join

const arr = ['hello', 'world', 18];
console.log(arr.join(' ')) // hello world 18
console.log(arr); // ['hello', 'world', 18]

concat

const arr = [1, 2, 3, 4];
const arr1 = ['hello', 'world', 18];
const arr2 = [5, 6, 7];
console.log(arr.concat(arr1, arr2).concat(8, 9)); // [1, 2, 3, 4, 'hello', 'world', 18, 5, 6, 7, 8, 9]
console.log(arr); // [1, 2, 3, 4]

slice

const arr = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
console.log(arr.slice(1, 5)); // [1, 2, 3, 4]
console.log(arr);// [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

map

const arr = [1, 2, 3, 4];
console.log(arr.map(i => i * 2));  // [2, 4, 6, 8]
console.log(arr); // [1, 2, 3, 4]

every

const arr = [1, 2, 3, 4];
console.log(arr.every(i => i > 3)); // false
console.log(arr.every(i => i > 0)); // true
console.log(arr); // [1, 2, 3, 4]

some

const arr = [1, 2, 3, 4];
console.log(arr.some(i => i > 4)); // false
console.log(arr.some(i => i > 0)); // true
console.log(arr); // [1,2,3,4]

filter

const arr = [1, 2, 3, 4];
console.log(arr.filter(i => i > 3)); // [4]
console.log(arr); // [1, 2, 3, 4]

forEach

const arr = [1, 2, 3, 4];
const arr1 = [];
console.log(arr.forEach(i => {
   arr1.push(i * 4);
}));
console.log(arr1); // [4, 8, 12, 16]
console.log(arr); // [1, 2, 3, 4]

reduce

const arr = [1, 2, 3, 4];
console.log(arr.reduce((prev, cur) => prev + cur, 0)); // [1, 2, 3, 4]
console.log(arr); // 10

改变原数组

pop

const arr = [1, 2, 3, 4];
const newArr = [];
console.log(arr.pop()); // 4
console.log(newArr.pop()); // undefined
console.log(arr); // [1, 2, 3]
console.log(newArr); // []

push

const arr = [1, 2, 3, 4];
console.log(arr.push(5)); // 5
console.log(arr); // [1, 2, 3, 4, 5]

shift

const arr = [1, 2, 3, 4];
console.log(arr.shift()); // 1
console.log(arr); // [2, 3, 4]

unshift

const arr = [1, 2, 3, 4];
console.log(arr.unshift(5, 6)); // 6
console.log(arr); // [5, 6, 1, 2, 3, 4]

reverse

const arr = [1, 2, 3, 4];
console.log(arr.reverse()); // [4, 3, 2, 1]

sort

const arr = [1, 2, 3, 4, 10, 12, 22];
console.log(arr.sort()); // [1, 10, 12, 2, 22, 3, 4]
console.log(arr) // [1, 10, 12, 2, 22, 3, 4]

splice

const arr = [1, 2, 3, 4];
console.log(arr.splice(1, 2, 10, 12)); // [2, 3]
console.log(arr); // [1, 10, 12, 4]