How to define multiple arrays in javascript

Question

So I have some code here: First a simple random # generator and a array-choosing function:

function Rand(min, max) {
 return parseFloat(Math.floor(Math.random() * max - min + 1))) + parseFloat(min);
}
function Choose(arr) {
 //Returns an element from an array at random.
 return arr[Math.floor(Math.random() * arr.length)];
}

and second a Card shuffler:

function CardDeck() {
 var Cd = ["Ace", "2", "3", "4", "5", "6", "7", "8", "9", "10", "Jack", "Queen", "King"];
 var H = [];
 var S = [];
 var D = [];
 var C = [];
 var Result = [];
 var Dk = document.getElementById("Deck Count").value;
 for (i = 0; i < Cd.length; i++) {
 S[i] = Cd[i] + " of Spades";
 H[i] = Cd[i] + " of Hearts";
 C[i] = Cd[i] + " of Clubs";
 D[i] = Cd[i] + " of Diamonds";
 }
 if (Dk == "4") {
 P = S.concat(C, D, H);
 } else if (Dk == "5") {
 var St = [];
 for (i = 0; i < Cd.length; i++) {
 St[i] = Cd[i] + " of Stars";
 }
 P = S.concat(C, D, H, St);
 } else if (Dk == "6") {
 var Rk = [];
 var Wh = [];
 for (i = 0; i < Cd.length; i++) {
 Rk[i] = Cd[i] + " of Rackets";
 Wh[i] = Cd[i] + " of Wheels";
 }
 P = S.concat(C, D, H, Rk, Wh);
 }
 for (i = 0; i < Dk * Cd.length; i++) {
 var Q = Choose(P);
 R = P.indexOf(Q);
 Result[i] = (i + 1) + ": " + Q;
 P = P.slice(0, R).concat(P.slice(R + 1));
 }
 document.getElementById("Cards").innerHTML = Result.join("\n");
}

Is there an easy way to make this faster or at least declare the arrays faster instead of just doing a=[],b=[]... for each as that can be time-consuming and tedious.

Additionally, is there a way to get a better RNG with a longer period in base JS (no libraries, as this was built on base JS)

• Spencer Wieczorek: It's not faster necessarily, but it would probably be more convenient to use an object with these arrays as properties, or use an array of arrays.

Answer 1

You can avoid typing var over and over like this: var H=[], S=[], D=[], C=[]; But otherwise it's hard to get more concise than what you have.

Answer 2

If you store the suit names in another array it eliminates a lot of variables; then using apply with concat can get them all into Result in one shot:

function CardDeck() {
 var Cd = ["Ace", "2", "3", "4", "5", "6", "7", "8", "9", "10", "Jack", "Queen", "King"];
 var Result = [];
 var Dk = document.getElementById("Deck Count").value;
 // Put the suit names into a new array
 var suitNames = [" of Spades", " of Hearts", " of Clubs", " of Diamonds"];
 if (Dk == "5") {
 suitNames.push(" of Stars");
 } else if (Dk == "6") {
 suitNames.push(" of Rackets");
 suitNames.push(" of Wheels");
 }
 // Create all suit stacks as an array of arrays
 var suits = [];
 for (var i = 0; i < Cd.length; i++) {
 for(var j = 0; j < suitNames.length; j++) {
 if(i===0) suits.push([]);
 suits[j].push(Cd[i] + suitNames[j]);
 }
 }
 // Combine all cards into a single array
 var P = Array.prototype.concat.apply([], suits);
 // Shuffle the deck
 for (i = 0; i < P.length; i++) {
 var Q = Choose(P);
 R = P.indexOf(Q);
 Result[i] = (i + 1) + ": " + Q;
 P = P.slice(0, R).concat(P.slice(R + 1));
 }
 document.getElementById("Cards").innerHTML = Result.join("\n");
}

Here's a running sample: https://jsfiddle.net/b4rf3ne2/

Is that closer to what you're looking for?

• Malachi Wadas: Yes this is perfect as it also allows for many suits to be made at once! Thank you.

Answer 3

You could do something like: declare one array-root, then declare a lot of subarrays in a for loop:

var arrays = [];
var nmbOfAr = 20;
for(int i = 0; i < nmbOfAr; i++){
 arrays[i] = [];
}

Answer 4

Using ES6 I think we can make marginal improvements.

let {S, H, C, D} = Cd.reduce((state, cardType, idx) => {
 state.S.push(cardType + ' of Spades');
 state.H.push(cardType + ' of Hearts');
 state.C.push(cardType + ' of Clubs');
 state.C.push(cardType + ' of Diamonds');
 return state; 
}, {
 S: [],
 H: [],
 C: [],
 D: [],
});