gistfile1.js

"use strict";
function bagGenerator(pieces, exclusions) {
    var buf = pieces.slice(),
        size = pieces.length,
        ptr = -1;

    var shuffle = function () {
        for (var t, j, i = 1; i < size; i++) {
            j = Math.random() * (i+1) |0;
            t = buf[i];
            buf[i] = buf[j];
            buf[j] = t;
        }
        ptr = size;
    };
    
    shuffle();
    
    // as written, this will yield an infinite loop if all pieces
    // in the 'pieces' array are also members of the 'exclusions' array
    while (exclusions.indexOf(buf[size - 1]) > -1) {
        buf.unshift(buf.pop());
    }
    
    return function () {
        var ret = buf[--ptr];
        if (!ptr) shuffle();
        return ret;
    };
}