https://www.reddit.com/r/dailyprogrammer/comments/3ofsyb/20151012_challenge_236_easy_random_bag_system/

tetris-random-bag.js

var chars = 'OISZLJT';

// Generates a string of tetris pieces of n-length
function tetris(n) {
    var pieces = chars.split('');
    return _.map(_.times(n, function() {
        var piece = _.sample(pieces);
        pieces = _.without(pieces, piece);
        if (pieces.length <= 0) {
            pieces = chars.split('');
        }
        return piece;
    })).join('');
}

// Verify that the tetris string is valid
// i.e. no more than 1 unique character per
// seven characters.
function verify(s) {
    var valid = true;
    var chunks = _.chunk(s, 7);
    for (var i = 0; i < chunks.length; i++) {
        var chunk = chunks[i];
        var sorted = chunk.sort();
        var curr = sorted[0];
        for (var j = 1; j < sorted.length; j++) {
            if (curr === sorted[j]) {
                valid = false;
                break;
            } else {
                curr = sorted[j];
            }
        }
    }
    return valid;
}

var result = tetris(50);
console.log(result, verify(result));