Several ways to weigh JS array

In some background languages, several methods are built in to handle duplicate data in arrays or collections. But there is no similar method in JS, there are some methods on the Internet, but not enough detail. Some of the code comes from the network. The individual totals are as follows: There are roughly 4 ways

1) Use two cycles to compare the original notation
Easy to understand efficiency is relatively low

1Array.prototype.unique1 =function () {2     varres = [ This[0]]//result Array3      for(vari = 1; I < This. length; i++) {4         varrepeat =false;5          for(varj = 0; J < Res.length; J + +) {6             if(Res[j] = =Res[i]) {7repeat =true8                  Break9             }Ten         } One         if(!repeat) { A             //do not repeat the push result array -Res.push ( This[i]) -         } the     } -     returnRes -}

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2) after sorting, compare adjacent positions for equality, if equal to push to result array

1Array.prototype.unique2 =function () {2      This. Sort ();3     varres = [ This[0]];4      for(vari = 1; I < This. length; i++) {5         if( This[i]!== res[res.length-1]) {6Res.push ( This[i]);7         }8     }9     returnRes;Ten}

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3) Use IndexOf to determine if the element exists indexOf because it will also traverse once, so, not recommended
IndexOf
A the position of the first occurrence of a specified string value in the string.
The string value retrieved by B does not appear, then the method returns-1.

1 //1)2Array.prototype.unique3 =function () {3     varres = [ This[0]]//result Array4      for(vari = 1; I < This. length; i++) {5         if(Res.indexof ( This[i]) = =-1) n.push ( This[i]);6     }7     returnRes8 }9 //2)TenArray.prototype.unique4 =function () { One     varres = [ This[0]] A      for(vari = 1; I < This. length; i++) -         if( This. IndexOf ( This[i]) = = i) N.push ( This[i]) - } the returnRes -}

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4) Use object same-over property to detect high efficiency, but relatively high memory (space change time) recommended

1Array.prototype.unique5 =function () {2     varobj = {}3     varres = []4      for(vari = 0; I < This. length; i++)5         if(!obj[ This[i]]) {6Res.push ( This[i])7obj[ This] = 18         }9 }Ten returnRes One}

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If there is a good way to welcome the supplement

Several ways to weigh JS array