Functional programming, particularly higher level functions, works heavily with lists of data.

In this example, two separate artwork lists have the same initial state.The JavaScript array slice method is one of the most powerful and commonly used built-ins in the JavaScript language.Īnd with the rise of React and other functionally oriented JavaScript practices, it is becoming even more important, for 2 key reasons: When updating nested state, you need to create copies from the point where you want to update, and all the way up to the top level. Another person’s artwork list may point to the same element of the array! This is why you need to be careful when changing nested fields like list. They might appear to be “inside” in code, but each object in an array is a separate value, to which the array “points”. Objects are not really located “inside” arrays. This is a state mutation, which you should avoid! You can solve this issue in a similar way to updating nested JavaScript objects-by copying individual items you want to change instead of mutating them. So by changing en, you are also changing en.

When dealing with arrays inside React state, you will need to avoid the methods in the left column, and instead prefer the methods in the right column:Ĭoncat, spread syntax ( example)Īlternatively, you can use Immer which lets you use methods from both columns.Īlthough nextList and list are two different arrays, nextList and list point to the same object. Here is a reference table of common array operations. Then you can set your state to the resulting new array. To do that, you can create a new array from the original array in your state by calling its non-mutating methods like filter() and map(). Instead, every time you want to update an array, you’ll want to pass a new array to your state setting function. This means that you shouldn’t reassign items inside an array like arr = 'bird', and you also shouldn’t use methods that mutate the array, such as push() and pop(). Like with objects, you should treat arrays in React state as read-only.

In JavaScript, arrays are just another kind of object. How to make array copying less repetitive with Immer.How to update an object inside of an array.How to add, remove, or change items in an array in React state.

Slice in react js