How to toggle an array item with Javascript in React State

by Vincent Will

In this short article I will demonstrate how to write a function to toggle array items with Javascript and inside of React state.

First of all let’s have a look how to toggle an array item with Javascript (ES6):

function toggleArrayItem(arr, item) {
    arr.includes(item)
        ? arr.filter(i => i !== item) // remove item
        : [ ...arr, item ]; // add item
}

This function will get an array and the item to be toggled. The includes checks if the array already has the item. If yes then it uses filter to remove it. If not it uses the spread operator to create a new array containing the values of the provided array plus the new item.

Now let’s use this function with React State:

onToggleArray = item => {
    this.setState(state => {
        const arr = state.arr.includes(item)
            ? arr.filter(i => i !== item) // remove item
            : [ ...arr, item ]; // add item
        return {
            arr,
        };
    });
}

Since it’s not allowed to mutate the state directly, it’s not possible to just push an item to an array. So we use our function to create a new array based on the previous state. Then we’ll add this new array to the state.