一下午写了好几道题,都只会用push方法,我没救了

function concat(arr1, arr2) {
    var arr3 = [ ];
    for(i = 0; i < arr1.length; i++){
      console.log(arr1[i]);
      arr3.push(arr1[i]);
    }
    
    for(j = 0; j < arr2.length; j++){
      console.log(arr2[j]);
      arr3.push(arr2[j]);
    }
    return arr3;
}
console.log(concat([1, 2, 3, 4], ['a', 'b', 'c', 1]));