Chunk an array of objects and add empty arrays at the end

I need to chunk an array of objects so i write:

function conditionalChunk(array, size, rules = {}) {
    let copy = [...array],
        output = [],
        i = 0;

    while (copy.length)
        output.push(copy.splice(0, rules[i++] ?? size))


    return output
}

and it works fine if I have rules like { 0: 2, 1: 2 }

 const input = [[1,2,3],[4,5,6,7]],
                output = conditionalChunk(input.flat(), 3, { 0: 2, 1: 2 });
          
    // OUTPUT: [[1,2],[3,4],[5,6,7]]

but when I have rules at the end like { 0: 2, 1: 2, 2:0, 5:0 } my function ignore to create empty arrays at the end.

the output I need is:

const input = [[1,2,3],[4,5,6,7]],
                    output = conditionalChunk(input.flat(), 3, { 0: 2, 1: 2, 2:0, 5:0 });
              
        // OUTPUT: [[1,2],[3,4],[],[5,6,7],[]]

so I just need to not ignore rules for empty arrays at the end of array. How I can do that?

Answer

Finally, you could check the keys of rules and if greater or equal to the next index of output push an empty array.

function conditionalChunk(array, size, rules = {}) {
    let output = [],
        i = 0;

    while (i < array.length)
        output.push(array.slice(i, i += rules[output.length] ?? size));
    
    let l = Object.keys(rules).reduce((l, v) => l + (v >= output.length), 0);

    while (l--) output.push([]);

    return output;
}

console.log(conditionalChunk([1, 2, 3, 4, 5, 6, 7], 3, { 0: 2, 1: 2 })); // [[1,2],[3,4],[5,6,7]]
console.log(conditionalChunk([1, 2, 3, 4, 5, 6, 7], 3, { 0: 2, 1: 2, 2: 0, 5: 0 })); // [[1,2],[3,4],[],[5,6,7],[]]
console.log(conditionalChunk([1, 2, 3, 4, 5, 6, 7], 3, { 0: 0, 1: 2, 8: 0, 7: 0, 9:0, 20:0 }));

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