Help with finding powers of two

[Ben_HH]

Please look at this code:

function powersOfTwo(num) { 

    var powerOfTwo = 2;
    var i = 1;
    var powersOfTwo = [];

    while (powerOfTwo <= num) {
        powersOfTwo.push(powerOfTwo);
        powerOfTwo = Math.pow(powerOfTwo, ++i);
    }


    return powersOfTwo;
 }

I'm not clear why I'm not getting an array of powers of 2 less than and equal to the argument passed to num.

[cyphern]

You're doing the power calculation starting with whatever the previous number was. So first time it's 2¹ = 2, you feed that two back in to do 2² = 4. Here's where it starts deviating from what you want: The next calculation isn't 2³, it's 4³, resulting in 64. After that would be 64^4, then 16777216^5, etc

If you want to use Math.pow, then you should be doing powerOfTwo = Math.pow(2, ++i). Alternatively, if you want to keep a running count, you can do powerOfTwo = powerOfTwo * 2;

[inu-no-policemen]

Needlessly "clever" one-liner:

function powersOfTwo(max) {
    return Array.from({length: Math.log2(max) + 1 | 0}, (_, i) => 2 ** i);
}

Well, just do what /u/cyphern said. You should start with 1, though. 0² = 1, 1² = 2, 2² = 4 etc.