Array.from()

The array.from () method converts an array-like object or traversable object into a real Array.

What is an array-like object: an object with the length attribute.

ifArray.fromThe argument is a class array object

To convert an array-like object into a true array, the following conditions must be met:

  • The class array object must havelengthProperties. If not, an empty array is returned.
  • Object of the class arraykeyThe value must be a numeric or string number. Array elements areundefind

Example:

let array = {
  0: 'tom'.1: '65'.2: 'male'.3: ['jane'.'john'.'Mary'],}console.log(Array.from(array)); / / []

array.length = 4;

console.log(Array.from(array)); / / [' Tom ', '65' and 'male', [' Jane ', 'John', 'Mary']]

array.length = 5;
array.name = 'name';

console.log(Array.from(array)); / / [' Tom ', '65' and 'male', [' Jane ', 'John', 'Mary'], undefind]
Copy the code

ifArray.fromParameter is a string

let  str = 'hello world! ';
console.log(Array.from(str)) // ["h", "e", "l", "l", "o", " ", "w", "o", "r", "l", "d", "!"]
Copy the code

ifArray.fromThere are two parameters

The second argument, of type FUN, iterates through and processes each element, putting the processed value into the returned array.

let arr = [12.45.97.9797.564.134.45642]
let set = new Set(arr)
console.log(Array.from(set, item= > item + 1)) // [13, 46, 98, 9798, 565, 135, 45643]
Copy the code