JavaScript function to convert decimal number to binary
Strictly speaking, the number parameter isn't decimal; it's just an abstract number.  (This is more a criticism of the terminology in your question title than of your code.)  On the other hand, it is very weird that you coerce the result into a number (101010) rather than returning it as a string ('101010').

The implementation strategy, using Math.pow(…, 2), strikes me as extravagant.  You should be able to do this more efficiently using just arithmetic:

function convertBinary(number) {
    var binaryArr = [];
    for (; number; number /= 2) {
        binaryArr.push(number % 2);
    }
    return binaryArr.reverse().join('');
}


… or the same thing using bitwise operations:

function convertBinary(number) {
    var binaryArr = [];
    for (; number; number &gt;&gt;= 1) {
        binaryArr.push(number &amp; 1);
    }
    return binaryArr.reverse().join('');
}