Discussion on: Big-O Notation Cheatsheet

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Replies for: Most of JavaScript's functions on objects (Array objects included) are using some sort of a hashing algorithm to iterate over their properties [Cit...

And WOW, creating the array at the correct size really makes a huge difference:

function buildSquareMatrix2(items) {
    const len = items.length
    let matrix = new Array(len)

    for (let i = 0; i < len; i++) {
        const next = new Array(len)

        for (let j = 0; j < len; j++) {
            next[j] = items[j]
        }

        matrix[i] = next
    }
    return matrix
}

buildSquareMatrix        9504
buildSquareMatrix2       1528
buildSquareMatrix3       678

Less than 3x slowdown over .slice() while still allowing you to modify each value!