Why am I getting this output from this simple splice command?

Question

I have a small issue with understanding why I'm getting this output.

var arr = ["a", "b", "c", "d", "e", "f"];
arr.splice(2,0,"1");
console.log(arr);  

var arr2 = ["a", "b", "c", "d", "e", "f"];
arr2 = arr2.splice(2,0,"2");
console.log(arr2);

ouput is:

[ 'a', 'b', '1', 'c', 'd', 'e', 'f' ]
[]  

Why is the second line of output not:

[ 'a', 'b', '2', 'c', 'd', 'e', 'f' ]  

Is it an issue of assignment or what?

Answer 1

Reading about splice method. It returns

An array containing the removed elements. If only one element is removed, an array of one element is returned.

So by doing

arr2 = arr2.splice(2,0,"2");

you overwrite initial array arr with empty array [] returned by splice.

Answer 2

1 - The splice method Changes the content of an array

2 - The splice method returns the element removed - ** Not original Array **

Answer 3

So the problem is that only some methods return the original object after mutation as the return value. You can use a method decorator to keep access to the original object available even when the methods are designed differently.

const chainer = (target) =>
  new Proxy(target, {
    get: (_, prop, receiver) =>
        typeof target[prop] === 'function'
        ? new Proxy(target[prop], {
            apply: (f, _, args) => {
              f.apply(target, args);
              return {
                this: receiver,
                target,
              }
            },
          })
        : target[prop],
  });

const arr2 = chainer(["a", "b", "c", "d", "e", "f"])
    .splice(2,0,"1").this
    .splice(2,0,"2").target;
console.log(arr2);