From i to j - elements in a range starting with the ith element and ending with the jth element: arr.slice(i, j + 1) Remember the “cut to the left” exclusion rule means that to get the ith element, we need to add one (1) to our second argument.ģ. From the beginning to i - elements in range starting with the beginning of the array and ending with the ith element: arr.slice(0, i + 1) It only takes one argument-the starting index-and includes everything after.Ģ. From i to the end - elements in a range starting with the ith element, ending with the last element in the array: arr.slice(i) For any array, where i and/or j is an index, and n is a number of elements, you can remember a few common operations as follows:ġ. So, I wanted to include a sort of cheat sheet that translates the desired outcome from English to JavaScript. However, when I was learning, it would still take a few precious seconds for me to reason through the arguments and methods I needed. Now, hopefully, you have a slightly better grasp on slice(). splice() can also take a third argument that tells the method to insert a given element after the index specified in the first argument.
This means while the above example ( slice(1, 6)) would return, s p lice(1, 6) will return. splice() ’s second argument is not an index, but a number of elements to be removed.
So splicing is like slicing and then popping the slice… Confusing? You were warned.Ģ. It removes the last element from an array (i.e., the element pops off). But here: the ‘p’ in s plice reminds me of the pop() method, another method beginners are likely to have encountered. Warning: My mnemonics, like many folks’, are idiosyncratic, so the following may be completely unhelpful to you. This means it alters the original array, in this case by removing the elements in the specified range. However, there are some key distinctions in their behavior:ġ. They are both built-in array methods, both return a subarray from a specified range, and their names are awfully similar. splice()Īnother likely source of confusion for a coding novice is the existence of slice()’s cousin, splice(). When I was learning, I found it helpful to think about slicing as a physical activity where the cut is always made to the left of the specified index as shown below: let arr= ` arr.slice(1, 6) //=> // | slice() vs. The first argument (the start of the subarray) is inclusive, while the second argument is exclusive. It can be hard to remember at first which indices are required for the range we need. This will be an important distinction in the following section. Notice first that the start and end (our two arguments) represent the index of an item.
“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…" Below, you'll find a few tips I wish I had known when I started slicing, splicing, and dicing* arrays in JavaScript. It’s an operation so common that many languages, like Python, use bracket notation to make slicing almost as easy as retrieving an element (i.e., arr to retrieve element at index 3, arr to retrieve elements from index 0 to index 3).
Most (all?) high-level programming languages have a similar method called by a similar name. JavaScript’s slice() method was one of the first built-in methods I memorized after maybe length(). The ability to extract subarrays is key to array manipulation.
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