Move Javascript array key forward?

byMR

August 19, 2023

I have 2 items in my object, 1 and 2.

structure concept

I want to add to each item a second frame
and to move the:

second frame -> third frame,

third frame -> fourth frame

(notice that I simplified the question, so I would normally have many frames it shouldn’t be harcoded)

window.onload = function() {
    localStorage.clear();
    const myObject = {
        "1": {
            keyframes: [
                {"posX": "0", "posY": "0"},
                {"posX": "150", "posY": "0"},
                {"posX": "300", "posY": "0"}
            ]
        },
        "2": {
            keyframes: [
                {"posX": "0", "posY": "0"},
                {"posX": "150", "posY": "0"},
                {"posX": "300", "posY": "0"}
            ]
        }
    };
    window.localStorage.setItem("myObject", JSON.stringify(myObject));
}

I tried foreach loop but don’t know how to implement array modifications from other stackoverflow questions…

>Solution :

Use Array::splice() to insert an element to an array at a specific index:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/splice

const myObject = {
  "1": {
      keyframes: [
          {"posX": "0", "posY": "0"},
          {"posX": "150", "posY": "0"},
          {"posX": "300", "posY": "0"}
      ]
  },
  "2": {
      keyframes: [
          {"posX": "0", "posY": "0"},
          {"posX": "150", "posY": "0"},
          {"posX": "300", "posY": "0"}
      ]
  }
};

const frame = {newFrame: true}; // fill it with your needed data

Object.values(myObject).forEach(({keyframes}) => keyframes.splice(1, 0, frame)); // insert as a second frame

$result.textContent = JSON.stringify(myObject, null, 4);