(JS) array de duplication

1. Use new Set()

var arr = [1,2,3,4,5,5,4,3,2,11,3,22,11,11,22];
    let c = new Set(arr); 

new Set() Method can add all non repeating values to the new Set in , Then return

2. Use fliter() Method

var arr = [1,2,3,4,5,5,4,3,2,11,3,22,11,11,22];
let x = arr.filter(function(val,index),array) {
	return array.indexOf(val)=== index;
}

filter() Method can return the value that meets the condition . Use indexOf lookup array Whether the index of the current value in is equal to index, If equal to, it means that the array does not exist val, Return once , If there is , Then don't go back .

3. Use circular judgment

  var arr = [1,2,3,4,5,5,4,3,2,11,3,22,11,11,22];
    let newArr = [];
    for(let i = 0; i<arr.length; i++) {
      if(newArr.indexOf(arr[i]) === -1) {
        newArr.push(arr[i]);
      }
    }

Create a new empty array , And then use indexOf Judge , If it is equal to -1, Indicates that there is no current item in the empty array , be push Enter new array . This method can only judge simple type values , If judgment is needed undefined and NaN,Null You need to add additional judgment conditions .

4. Use reduce() Method to remove duplication

var arr = [1, 2, 3, 4, 5, 5, 4, 3, 2, 11, 3, 22, 11, 11, 22];
  let x = arr.reduce(function(accumulation, current) {
    if (!accumulation.includes(current)) {
      accumulation.push(current);
    }
    return accumulation;
  }, []);

reduce() The method is ES6 New array method added in , It can be used for cumulative calculation , It can also be used to judge some items