JS array de duplication

1、 Traverse + Array.prototype.indexOf duplicate removal .

var arr = [1, '1', 1, 'str', NaN, NaN, null, null, undefined, undefined];
function deleteDuplicate(a) {
    
  if( Object.prototype.toString.call( a ) !== '[object Array]' || !a.length ) {
    return a;// The array 、 Empty array directly returns 
  }
  var tmp = [ a[0] ];// Store the first element of the original array 
  for(var i = 1; i < a.length; i++) {
   // Start traversing from the second 
    if( tmp.indexOf( a[i] ) === -1 ) {
      tmp.push( a[i] );
    }
  }
  return tmp;
}
deleteDuplicate( arr );
//[1, "1", "str", NaN, NaN, null, undefined]
// You can't get rid of it  NaN, have access to  ES2016  The introduced array method 
//[1, 2, NaN].includes( NaN ) === true

2、 For pure numbers , Pure character array , You can use js Object properties , Object key is unique and character .

var arr = [1, 2, 4, 2, 4, 3, 1];
function deleteDuplicate(a) {
    
  if( Object.prototype.toString.call( a ) !== '[object Array]' || !a.length ) {
    return a;
  }
  var obj = {}, tmp = [];
  for(var i = 0; i < a.length; i++) {
    obj[ a[i] ] = a[i];
  }
  for( var key in obj ) {
    tmp.push( obj[key] );
  }
  return tmp;
}
deleteDuplicate( arr );
//[1, 2, 3, 4]
// Because the keys of traditional objects are characters ,obj[1]  and  obj['1']  It's the same effect , And the original order cannot be guaranteed 

3、ES6 Provides Map data structure . It's like an object , It's also a set of key value pairs , however “ key ” Is not limited to strings , Various types of values （ Including objects ） Can be used as a key . in other words ,Object Structure provides “ character string — value ” Corresponding ,Map Structure provides “ value — value ” Corresponding , Is a more perfect Hash Structure implementation . If you need “ Key value pair ” Data structure of ,Map Than Object More appropriate , also Map The traversal order of is the insertion order .

let arr = [NaN, 1, [1], [1], 1, '1', 4, 1, 2, 4, 5, 5, NaN, NaN, null, null, undefined, undefined];
function deleteDuplicate(a) {
    
  if( !Array.isArray( a ) || !a.length ) {
    return a;
  }
  let map = new Map();
  a.forEach( value => map.set(value, value) );
  return Array.from( map.values() );// return [ ...map.values() ];
}
deleteDuplicate( arr );
//[NaN, 1, Array(1), Array(1), "1", 4, 2, 5, null, undefined]
//Map  The traversal order of is the insertion order 

4、ES6 Provides a new data structure Set. It's like an array , But the values of the members are unique , There are no duplicate values .

let arr = [NaN, 1, [1], [1], 1, '1', 4, 1, 2, 4, 5, 5, NaN, NaN, null, null, undefined, undefined];
function deleteDuplicate(a) {
    
  if( !Array.isArray( a ) || !a.length ) {
    return a;
  }
  let set = new Set( a );
  return Array.from( set );// return [ ...set ];
}
deleteDuplicate( arr );
//[NaN, 1, Array(1), Array(1), "1", 4, 2, 5, null, undefined]