I recently ran into an issue where I needed to filter out some items in a nested array inside an object of arrays in JavaScript. After trial and error, I found out how to extract the information that I needed.

Suppose we have an object of arrays which has users and the sporting equipment that they have borrowed. Here is our data object:

const data = {
    users: [

    {
            "id": "123",
            "name": "John Smith",
            "items": [
                {
                    "id": 1,
                    "name": "Soccer ball",
                }                
            ]
    },
    {
            "id": "456",
            "name": "Steve Johnson",
            "items": [
                {
                    "id": 2,
                    "name": "Basketball",
                }
            ]
    },
    {
            "id": "789",
            "name": "Leslie Thompson",
            "items": [
                {
                    "id": 3,
                    "name": "Football",
                }
            ]
    }
  ]
};

Let’s say we want to find out who borrowed the basketball. We first start by using the filter function in order to filter out the data that we want:

const output = data.users.filter(x => x.items.every(y => y.name.includes("Basketball")));

We use two functions in addition to filter. First, we use the every function. The every function is used to test whether the parameters that you pass inside it exist. It returns a boolean. The includes function searches inside an array to see whether the value that you are looking for exists.

If we console.log(output) we get the following:

(1) [Object]

    0: Object

        id: "456"

        name: "Steve Johnson"

        items: Array(1)

            0: Object

                id: 2

                name: "Basketball"