How to Safely Delete Items from a State Array in React?

Deleting Items from an Array in React: A Guide

In React, managing state is crucial for maintaining the integrity of your application's behavior and user experience. A common scenario involves the manipulation of arrays in state, such as adding, removing, or updating items.

To understand how to delete an item from a state array, let's consider a simple example:

You want to have a list of three people: Bob, Sally, and Jack, stored in a state array. You need to be able to remove any of them from the list, and when removed, the array should not have any empty slots.

In your React component, you may have the following code:

getInitialState: function() {
  return{
    people: [],
  }
},

selectPeople(e){
  this.setState({people: this.state.people.concat([e.target.value])})
},

removePeople(e){
  var array = this.state.people;
  var index = array.indexOf(e.target.value); // Let's say it's Bob.
  delete array[index];
},

However, this implementation of the removePeople() function won't work as intended when called. The reason lies in the way React handles state mutation.

Never Directly Mutate State in React

When updating an object or array in state, it's essential to create a new copy. Mutating the original state object or array directly can lead to unexpected behavior and potential bugs.

In this case, deleting an element from the array directly, which modifies the original state object, doesn't trigger an update of the state in React. The state remains unchanged, and the UI won't reflect the removal of Bob from the list.

Using Array.prototype.filter() for Safe Removal

To remove an item from a state array in a manner compatible with React, there are several options. One effective method involves utilizing Array.prototype.filter().

removePeople(e) {
    this.setState({people: this.state.people.filter(function(person) { 
        return person !== e.target.value 
    })});
}

This approach creates a new array with the filtered results. In this case, it filters out the person with the target value, effectively removing it from the list. The resulting new array is then set as the state, triggering the necessary UI updates to reflect the removal of the item.

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