Slice array items

dividedArray.js

const arr = [1,2,3,4];
const splitedArrItems = [];
const splitIdx = 2;

const indice = arr.length/splitIdx;

for (let i = 0; i < indice; i++) {
    splitedArrItems.push(arr.splice(0, splitIdx));
}

const obj = {}; // {0: '[1,2]', 1: '[3,4]'}

splitedArrItems.forEach((e, i) => {
    // insert code logic here
    obj[i] = JSON.stringify(e);
});

// reverse process
const joinedObjItems = []; // [[1,2], [3,4]]
for (let itemObj in obj) {
    joinedObjItems.push(JSON.parse(obj[itemObj]))
}

joinedObjItems.flat() // [1,2,3,4]