shuffleArray.js

// Based on Fisher–Yates shuffle ( https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle ) 
// and Shuffling an Array in JavaScript ( https://www.kirupa.com/html5/shuffling_array_js.htm )

// returns a new array shuffled
Array.prototype.shuffle = function() {
    let tmpArray = [ ... this ]; // create a copy of original array
    for( let i = tmpArray.length - 1; i; i -- ) {
        let randomIndex = ~~( Math.random() * ( i + 1 ) ); 
        [ tmpArray[ i ], tmpArray[ randomIndex ] ] = [ tmpArray[ randomIndex ], tmpArray[ i ] ]; // swap
    }
    return tmpArray;
};

// permanently shuffles the array
Array.prototype.permShuffle = function() {
    for( let i = this.length - 1; i; i -- ) {
        let randomIndex = ~~( Math.random() * ( i + 1 ) );
        [ this[ i ], this[ randomIndex ] ] = [ this[ randomIndex ], this[ i ] ]; // swap
    }
    return this;
};

/*
//Usage:
const arr = ( new Array( 5 ) ).fill( 0 ).map( ( d, i ) => i ); 
console.log( arr ); // [0, 1, 2, 3, 4]

console.log( arr.shuffle() ); // [0, 4, 1, 2, 3] <- returns a copy array shuffled
console.log( arr );  // [0, 1, 2, 3, 4] <- original array was not modified

console.log( arr.permShuffle() ); // [0, 1, 3, 4, 2] <- returns original array shuffled
console.log( arr ); // [0, 1, 3, 4, 2] <- original array was modified
*/