You just need to pass the elements you want to add to the array after the delete count. The method also allows you to add new elements right after the delete operation. How to remove and add array elements with splice() When you omit the removeCount parameter, splice() will remove all elements from the start index to the end of the array. For example, to remove only one element, you can pass the number 1 like this: let months = Ĭonsole.log(months) // Remove only one element from the array You can also define how many elements you want to remove from the array by passing a second number argument known as removeCount. In the code above, the number 2 is passed to the method, which means splice() will start removing elements from index 2. The splice() method needs at least one parameter, which is the start index where the splice operation starts. You can use the splice() method to remove the day names from the months method and add it to a new array at the same time: let months = Ĭonsole.log(days) // Creating an array of days How to remove array elements with splice()įor example, suppose you have an array named months but you have some day names in the array as follows: let months = A mixed array of month and day names Let's start with removing elements from an array first. In this tutorial, you will learn how you can remove, add, or replace elements of an array using the splice() method. This method modifies the original array and returns the removed elements as a new array. It lets you change the content of your array by removing or replacing existing elements with new ones. There has been a huuuge BENCHMARKS thread, providing following information:įor blink browsers slice() is the fastest method, concat() is a bit slower, and while loop is 2.4x slower.įor other browsers while loop is the fastest method, since those browsers don't have internal optimizations for slice and concat.The splice() method is a built-in method for JavaScript Array objects. If you want to keep the original array, clone the array, then use splice on the cloned array.įrom an SO question about cloning arrays: Note that this modifies your original array. Let leftSide = letters.splice(0, Math.ceil(letters.length /2)) Let leftSide = myArray.splice(0, Math.ceil(myArray.length / 2)) įor example: let letters = Let arraySecondHalf = yourArray.slice(halfwayThrough, yourArray.length) Let arrayFirstHalf = yourArray.slice(0, halfwayThrough) or instead of floor you can use ceil depending on what side gets the extra data Let halfwayThrough = Math.floor(yourArray.length / 2) You can get around this by using slice instead of splice Example let yourArray = props.someArray log the original object and see that its value has been changedĬonsole.log(myObj) // will log Īs you can see the object myObj had the value of key changed as well. change the value of a key in the new const assign a new const to the object (this is assigned by reference) ![]() ![]() This means that if you use the original reference you will get the new value. When you mutate an object or array you change that original reference. You can always tell if a method will mutate by whether or not it returns a new array or object. ![]() Using an array method like splice will cause the original array to be manipulated. What is a Mutation?Ī mutation is when you change a non primitive, like an object or array. If you need to avoid mutations, for example if you have to split an array in react you don't want to mutate the original or it could lead to some very strange behaviour in your app.
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