[рони]

gsdev99,

const arr = [
    [{id: 1, value: 'item 1'}, {id: 2, value: 'item 2'}, {id: 3, value: 'item 3'}, {id: 4, value: 'item 4'}],
    [{id: 1, value: 'item 1'}, {id: 2, value: 'item 2'}],
    [],
    [{id: 1, value: 'item 1'}, {id: 2, value: 'item 2'}, {id: 3, value: 'item 3'}]
];
const length = arr.reduce((l,{length})=>Math.max(l,length),0);
const arrNew = arr.map(a => Array.from({ length }, (v, k) => a[k] ? {...a[k]} : {id: ++k, value: '-'}));

console.log(arrNew)