const arr = ['a','b','c','d','e','f','g'];


const chunkArray = (array, length) => {
    let newArr = [];
    let temp = [];

    for(let i = 0; i < array.length; i++){
        temp.push(array[i]);
        if((i+1)%length===0 && i!==0){
            newArr.push(temp);
            temp = [];
        }
    }
    newArr.push(temp);
    return newArr;
}

console.log(chunk(arr, 4))