Converts a decimal array to a binary array, eg [12,13,5,4] == [0, 0, 1, 1, 0, 0, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0] f2 is almost 6x faster in v8.

faster-decimal-conversion.js

var f1 = function (a) {
    return a.map(function (n) {
        // convert number to decimal reverse the order then left pad it to a byte
        return String((n).toString(2).split('').reverse().join('') + Array(8 + 1).join("0")).substr(0, 8);
    }).join('')
        .split('')
        .map(function (n) {
            return +n; // convert each of the numbers to int
        });
};


var f2 = function (bitRow) {
    var calcArray = new Array(bitRow.length * 8),
        pos = 0,
        len = bitRow.length;
    for (var i = 0; i < len; i++, pos++) {
        var currentByte = bitRow[i];
        calcArray[pos] = (currentByte & 1);
        pos++;
        calcArray[pos] = (currentByte & 2) >> 1;
        pos++;
        calcArray[pos] = (currentByte & 4) >> 2;
        pos++;
        calcArray[pos] = (currentByte & 8) >> 3;
        pos++;
        calcArray[pos] = (currentByte & 16) >> 4;
        pos++;
        calcArray[pos] = (currentByte & 32) >> 5;
        pos++;
        calcArray[pos] = (currentByte & 64) >> 6;
        pos++;
        calcArray[pos] = (currentByte & 128) >> 7;

    }
    return calcArray;
};

console.time('Time f1');

for(var i=0;i<1000;i++) {
    f1([17, 160, 83, 41, 25]);
}
console.timeEnd('Time f1');

console.time('Time f2');

for(var i=0;i<1000;i++) {
    f2([17, 160, 83, 41, 25]);
}
console.timeEnd('Time f2');