So what happens if we add a negative number as the start parameter? If the start is negative, it will count backward from the end of the array and remove the elements. Also, if you add any number higher than the largest index number of the array, it will not affect the original array. If you add 0 as the start parameter without any other parameters, it will remove everything from the array and change it to an empty array. And you can see the removed item in the array, removedFruits. Since we haven't specified a second parameter, it has removed everything after index 2, including the index 2 element. In the above example, we have added the start parameter as 2, and that's where it has started removing things from this array. Let favoriteFruits = let removedFruits = favoriteFruits. You can check further details on these parameters below. The JS array splice method takes several arguments to decide which elements to delete, the delete count, and what elements to add. It will also return a new array with all the elements you have removed, which is helpful if you want to track what has been removed. This method modifies the array and does not create a new array. The splice() method in Javascript helps you add, update, and remove elements in an array. The slice() method is very useful for cloning an array, copying a portion of an array, and converting an array-like object into an array. This is very useful when you want to get the last element of the array, and then you just have to use -1. If we have given -2, it will return only. This will start counting from the end of the array and slice it (not the beginning from the array). In the above example, we have added a single argument as -3. Let favoriteFood = let slicedArray = favoriteFood. Also, If the arguments you pass are greater than the actual array, it will return an empty array. If you do not pass any arguments, the entire original array will be copied by default. The first argument is the startIndex, and the second is the endIndex. This method takes two optional arguments. Instead, it creates a new shallow copy of the original array. It does not modify or change the original array. The array slice javascript method copies a chunk (or slice) from an array and returns that copied part as a new array. I've put together this guide on these two methods so that you can slice and splice JavaScrips arrays like a pro. Javascript Slice() and splice() methods look similar, and they sound similar, so it's very easy to get confused and remember which is which. The two methods are among the most used array methods when it comes to adding, updating, or removing items in an array, and cloning an array or copying a portion of an array. Not that I'm using objects as if they are sets the key is the data I'm interested in, and the value is only a boolean flag to tell if it's been 'removed'.Do you find yourself looking up the difference between javascript splice () and splice() methods all the time? Since Array.splice() and Array.pop() tend to have pretty bad performance characteristics, I suggest replacing the () implementation with a simple overwrite-with-undefined, and updating all of our array iterations to test for undefined.Īlternatively, if elements are going to be created and deleted often, it might even be better to use objects, instead. Ok, now back to the issue with Array.splice() )

It also tells me that iterating an object with a for.in loop and 'removing' object properties by setting its value to 0 is going to be much faster than iterating arrays that need elements removed in ALMOST ALL CASES. This tells me arrays have strange scoping problems in Chrome. Now looking closely at group 3, both perform very well ~135MM and ~107MM respectively. The performance for the local scope test is HORRIBLE! ~11MM vs ~149MM (and pop is pretty bad too, at only ~16MM) Looking more closely at group 2, array-undefined is almost exactly the same as the global variation, except they access an array in different scopes. But that doesn't immediately discount object as being slower overall! Now in group 1, I have two numbers indicating the relative speed: array gives ~32MM, and object gives ~12MM, meaning object is over 2x slower. In my test on Chrome 27, global array-undefined was fasted for group 2, and object-zero was fasted for group three. The 'winners' from groups 2 and 3 can then be compared directly. pop vs array-undefined vs global array-undefined.First, the tests are useful to compare to one another in the following groups: These tests are not all apples-to-apples. Here is an interesting test case I made:

Array.splice() is used in our () (which is also quite handy). But it's awfully slow! It's the reason for the performance problems in ticket #103.

Javascript array splice efficiency