Summary of JavaScript method examples for removing duplicate elements from an array

Array deduplication;

The Array type does not provide a deduplication method. If you want to remove duplicate elements from the array, you have to find a way yourself:

Method one: Use the indexOf method;

var aa=[1,3,5,4,3,3,1,4]
function arr(arr) {
  var result=[]
  for(var i=0; i<arr.length; i++){
    if(result.indexOf(arr[i])==-1){
      result.push(arr[i])
    }
  }
  console.log(result)
}      
arr(aa)

Method two:

function unique(arr) {
  var result = [], isRepeated;
  for (var i = 0, len = arr.length; i < len; i++) {
    isRepeated = false;
    for (var j = 0, len = result.length; j < len; j++) {
      if (arr[i] == result[j]) {  
        isRepeated = true;
        break;
      }
    }
    if (!isRepeated) {
      result.push(arr[i]);
    }
  }
  return result;
}

The general idea is to move the array elements one by one Go to another array and check whether the element is duplicated during the transfer. If so, discard it directly. As can be seen from nested loops, this method is extremely inefficient. We can use a hashtable structure to record existing elements, so that we can avoid inner loops. It just so happens that implementing hashtable in Javascript is extremely simple. The improvements are as follows:

function unique(arr) {
  var result = [], hash = {};
  for (var i = 0, elem; (elem = arr[i]) != null; i++) {
    if (!hash[elem]) {
      result.push(elem);
      hash[elem] = true;
    }
  }
  return result;
}

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