Rotating a rectangular array in Javascript

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I am trying to make a tetris game. I am trying to work on a function that rotates a 2D variable array 90 degrees (or -90).

For example, given an array like:

"-T-",
"TTT"

I would like an output like:

"T-",
"TT",
"T-"

etc, etc.

I have tried this function:

function rotateN90(a){
    var temp = [];
    for(var x = 0; x<a[0].length; x++){
        temp.push("");
        for(var y = 0; y<a.length; y++){
            temp[x] += a[y][x];
        }
    }
    
    return temp;
}

but it does not give the desired result. While it does rotate the first T-Block example given -90 degrees once, afterwards it reverts to it’s original state.

Please help!

(PS: I am using KA’s processing environment, so I can’t use libraries)

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