js 1d array to 2d
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const arr = [1,2,3,4,5,6,7,8,9];
const newArr = [];
while(arr.length) newArr.push(arr.splice(0,3));
console.log(newArr);
// result: newArr = [[1,2,3],[4,5,6],[7,8,9]]
https://stackoverflow.com/questions/22464605/convert-a-1d-array-to-2d-array