How to check if an array is a subset of another array in JavaScript?

Question

Let's say I have two arrays,

var PlayerOne = ['B', 'C', 'A', 'D']; var PlayerTwo = ['D', 'C']; 

What is the best way to check if arrayTwo is subset of arrayOne using javascript?

The reason: I was trying to sort out the basic logic for a game Tic tac toe, and got stuck in the middle. Here's my code anyway... Thanks heaps!

var TicTacToe = {     PlayerOne: ['D','A', 'B', 'C'],   PlayerTwo: [],    WinOptions: {       WinOne: ['A', 'B', 'C'],       WinTwo: ['A', 'D', 'G'],       WinThree: ['G', 'H', 'I'],       WinFour: ['C', 'F', 'I'],       WinFive: ['B', 'E', 'H'],       WinSix: ['D', 'E', 'F'],       WinSeven: ['A', 'E', 'I'],       WinEight: ['C', 'E', 'G']   },    WinTicTacToe: function(){      var WinOptions = this.WinOptions;     var PlayerOne = this.PlayerOne;     var PlayerTwo = this.PlayerTwo;     var Win = [];      for (var key in WinOptions) {       var EachWinOptions = WinOptions[key];          for (var i = 0; i < EachWinOptions.length; i++) {           if (PlayerOne.includes(EachWinOptions[i])) {             (got stuck here...)           }          }         // if (PlayerOne.length < WinOptions[key]) {         //   return false;         // }         // if (PlayerTwo.length < WinOptions[key]) {         //   return false;         // }         //          // if (PlayerOne === WinOptions[key].sort().join()) {         //   console.log("PlayerOne has Won!");         // }         // if (PlayerTwo === WinOptions[key].sort().join()) {         //   console.log("PlayerTwo has Won!");         // } (tried this method but it turned out to be the wrong logic.)     }   },   }; TicTacToe.WinTicTacToe(); 

Answer 1

Here is the solution:

Using ES7 (ECMAScript 2016):

const result = PlayerTwo.every(val => PlayerOne.includes(val)); 

Snippet:

const PlayerOne = ['B', 'C', 'A', 'D']; const PlayerTwo = ['D', 'C'];  const result = PlayerTwo.every(val => PlayerOne.includes(val));  console.log(result);

Using ES5 (ECMAScript 2009):

var result = PlayerTwo.every(function(val) {    return PlayerOne.indexOf(val) >= 0;  }); 

Snippet:

var PlayerOne = ['B', 'C', 'A', 'D']; var PlayerTwo = ['D', 'C'];  var result = PlayerTwo.every(function(val) {    return PlayerOne.indexOf(val) >= 0;  });  console.log(result);

---

Here is answer the question at the comment below:

How do we handle duplicates?

Solution: It is enough to add to the above solution, the accurate condition for checking the number of adequate elements in arrays:

const result = PlayerTwo.every(val => PlayerOne.includes(val)      && PlayerTwo.filter(el => el === val).length        <=        PlayerOne.filter(el => el === val).length ); 

Snippet for first case:

const PlayerOne = ['B', 'C', 'A', 'D']; const PlayerTwo = ['D', 'C'];  const result = PlayerTwo.every(val => PlayerOne.includes(val)      && PlayerTwo.filter(el => el === val).length        <=        PlayerOne.filter(el => el === val).length );  console.log(result);

Snippet for second case:

const PlayerOne = ['B', 'C', 'A', 'D']; const PlayerTwo = ['D', 'C', 'C'];  const result = PlayerTwo.every(val => PlayerOne.includes(val)      && PlayerTwo.filter(el => el === val).length        <=        PlayerOne.filter(el => el === val).length );  console.log(result);