A, the find

The find () method returns the first element in the array that meets the criteria, or undefined if it does not

let arr = [1.2.3.4.5.6.7];
let result = arr.find(function (item) {
  return item > 4; })console.log(result);/ / 5
console.log(arr);/ /,2,3,4,5,6,7 [1]
Copy the code

Second, the filter

The filter() method returns a new array that filters all the elements in the array that meet the criteria, or returns an empty array if no symbol criteria are found.

let arr = [1.2.3.4.5.6.7];
let result = arr.filter(function (item) {
  return item > 4; })console.log(result);/ / [5, 6]
console.log(arr);/ /,2,3,4,5,6,7 [1]
Copy the code

Third, forEach

The forEach() method is used to call each element of the array once, but it does not return a value (or undefined, even if the callback has a return).

ForEach () does not perform callbacks on empty arrays.

let arr = [1.2.3.4.5.6.7];
let sum = 0;
let result = arr.forEach(function (item) { sum += item ; })console.log(result);//undefined
console.log(arr);/ /,2,3,4,5,6,7 [1]
console.log(sum);/ / 28
Copy the code

Fourth, the map

The map() method returns an array of elements that are filtered and processed by the callback, and the result is returned in a new array (if no value is returned, each element of the new array is undefined).

let arr = [1.2.3.4.5.6.7];
let result = arr.map(function (item) {
  return item*2; })console.log(result);/ / [14] 2,4,6,8,10.12.
console.log(arr);/ /,2,3,4,5,6,7 [1]
Copy the code