Create an instance of an object containing arrays as properties

Question

Create an instance of an object containing arrays as properties

Is there a way to initialize an object in JavaScript with properties that are arrays?

I am looking to create an object structured like this:

foo = { prop1: [0, 1], prop2: [1, 1], prop3: [0] }

My scenario is as follows:

- If a property doesn't exist, I want to create it as an array and add a number.

- If a property already exists, I need to push the number to that existing array without reinitializing it every time.

This is what I have attempted so far:

var obj = {};
arr.forEach(x => { !obj[x] && obj[x].push(1) });

However, I keep encountering this error:

Uncaught TypeError: Cannot read property 'push' of undefined

This error occurs because the property has not been initialized as an empty array beforehand.

javascript arrays object initialization

Answer 1

Answer №1

Here is a useful code snippet:

arr.forEach((item) => {object[item] = (object[item] || []).concat(1);})

If object[item] is undefined, it means that it has not been initialized yet. In this case, undefined || [] will result in an empty array [], to which you can then append the value 1, or any other desired data.

Answer 2

Here is a useful code snippet:

arr.forEach((item) => {object[item] = (object[item] || []).concat(1);})

If object[item] is undefined, it means that it has not been initialized yet. In this case, undefined || [] will result in an empty array [], to which you can then append the value 1, or any other desired data.

Answer 3

Answer №2

Hello, here is a potential solution for you:

let obj = {};
let arr = ["prop1","prop2","prop1","prop3"];
arr.forEach((x) => {
   if(obj.hasOwnProperty(x)) obj[x].push(1);
   else {
      obj[x] = [];
      obj[x].push(1);
   } 
})
console.log(obj);

If obj already has the property x (hasOwnProperty), push the value 1. Otherwise, initialize x as an array property and push 1.

Answer 4

Hello, here is a potential solution for you:

let obj = {};
let arr = ["prop1","prop2","prop1","prop3"];
arr.forEach((x) => {
   if(obj.hasOwnProperty(x)) obj[x].push(1);
   else {
      obj[x] = [];
      obj[x].push(1);
   } 
})
console.log(obj);

If obj already has the property x (hasOwnProperty), push the value 1. Otherwise, initialize x as an array property and push 1.

Create an instance of an object containing arrays as properties

Answer №1

Answer №2

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