What are the ways to remove duplicates from javascript arrays?

Removal method: 1. Use the "Array.from(new Set(arr))" statement; 2. Use the "[...new Set(arr)]" statement; 3. Use "arr.filter( (item,index)=>arr.indexOf(item)===index)" statement.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

Several ways to remove duplicates from JavaScript arrays

1. Array.from(new Set(arr))

const arr = [1, 2, 3, 2, 3];

Array.from(new Set(arr)); // [1, 2, 3]

Since the elements in the Set are unique, whether they are original values ​​or object references, deduplication can be achieved by converting the array into a Set object

Array.from Method can convert Set object into array

2, [...new Set(arr)]

const arr = [1, 2, 3, 2, 3];
[...new Set(arr)]; // [1, 2, 3]

Here is passed# The expansion syntax of ##ES6 converts the Set object into an array;

3. arr.filter((item, index) => arr.indexOf(item) == = index)

const arr = [1, 2, 3, 2, 3];

arr.filter((item, index) => arr.indexOf(item) === index); // [1, 2, 3]

indexOf method returns the first index (index) of the specified element in the array, if not, returns -1

So the index values ​​returned by each element in the arr array here through the

indexOf() method are 0 1 2 1 2

arr.forEach(item => console.log(arr.indexOf(item))); // 0 1 2 1 2

can be obtained through

indexOf To achieve deduplication, for example, the fourth element 2 in arr returns an index of 1 through indexOf, but its current index subscript is 3, which is not equal, indicating that the current This 2 element has appeared before, so it should be filtered out

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