#Return an array splice javascript how to#

We’ve understood different approaches and paradigms and have some more knowledge to take to tomorrow.

#Return an array splice javascript how to#

With that in mind - it’s time to conclude our post on how to remove an item, or “element”, from an array in JavaScript with the right tools. length property - see how it still says length: 4?! Another reason to avoid using delete. What’s more confusing is delete doesn’t affect the Array’s. I included this for clarity, it’s always great to see and understand what side effects your operations have. You’ll notice from the console.log output above that it completely blows away the key. Let’s take an array with a few string values:Ĭonst drinks = const id = 2 delete drinks // Array(4) // 0: 'Cola' // 1: 'Lemonade' // 3: 'Water' // length: 4 // _proto_: Array(0) console. This could be removing or replacing “elements”, as array items are known. Splice is a mutable method that allows you to change the contents of an array. The slice () method returns a shallow copy of a portion of an array into a new array object selected from start to end ( end not included) where start and end represent the index of items in that array. To remove an item from array via its index, we’ll first introduce the method and then investigate a better pattern using, a newer API. Without further ado, let’s first explore how to remove an item from an array in JavaScript by index and value. Each draw contains something unique! Arrays are virtual, so the size of the filing cabinet is up to you!īecause now you understand an array, you know how to work with one! Really, you can think of each index as a drawer in a filing cabinet. Ask for the index from your array and you’ll get back the item located at that index. With arrays this means when we need access to a value, whatever it may be (a primitive/object), it’s done via an “index lookup”. An index? Yes - 0, 1, 2, 3 and onwards! Array indexes start at zero. It is still an object, but the way that we “use” an array is by accessing properties on it that refer to an item in the array, via an index. The array object is special, it’s different. With that said, you now know how arrays are actually just objects - and objects have methods and properties. Both of these are inherited methods on the array object. The intention with this was to allow us to perform mutations and changes to our arrays with the nice utility functions “built-in”.Ī utility? Yes, for example () or (). 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.For example when we declare a new array via, that array contains Array.prototype properties and methods that allow us to interact with our array. 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.