This is completely different from Arrays in other languages, where an array of size n will have n storage spaces reserved for the elements (being pointers to objects or being native value types). Just the length property has a different initial value. Using or new Aray will both create Arrays with exactly the same memory footprint. It won't change the array length, nor will increasing the array length create any properties for the added index positions (sparse array). If you delete an indexed element from an array, it will just be deleted (and accessing this index later will return undefined, as it would do with any non-existent property). If the length is set, it is checked, whether the new value is smaller than the old one, and if so, all own properties with a property name that is a numerical value and >= the new length will be deleted. If a property is added to the object, its name is tested for being a numerical value and whether this value is >= the current array length. The difference is in the length property which has a spcieal setter method, and the different way of adding a new property. This final method is probably the most desirable.An Array is (aside from its prototype methods) not much more than a simple object. We can accomplish concatentation in a different syntax, again using the spread operator (.). If no second arg is provided, include the rest of the array. The first arg to slice is the first index to keep, all the way to the second arg, the index to stop at (and not include in the resulting array). We can accomplish this with an array method called concat. Since we'll have the before and after arrays, we'll also want to join them together at the end. So we can slice out the portion of the array we want to keep before and after the index for removal. There's another Array method called slice that allows you to select a portion of an array and return a new array. And it's somewhat inefficient in the new creation of and then immediate mutation of an array. But there's still mutation and room for bugs within the function body. This would protect a few things: keeping mutations inside a function body and not modifying the original data structures that were sent as arguments. > const fruits = undefined > const newFruits = undefined > newFruits. To do this, we could use a clone function or the spread operator (.) to copy the original array into a whole new array, the splice just the new array. We could simply do that: create a new array (a clone of the original) and mutate that instead of the original. You can also think of this as creating a new array without the elements you wanted removed. You need a new data structure because you cannot change the first - that would be mutation. To remove elements from an array in an immutable way, array copying is required. You can create more readable, predictable programs. Removal Without Mutationīut if you can avoid mutating the original array, that can often be better. The fruits array has been modified in place. If you had an array of const fruits = and wanted to remove apple, you'd call fruits.splice(2, 1) (index of 2, 1 element to remove). With splice, you tell the array at which index to start and how many elements to remove. Mutation means that the original array is changed in place. Default Mutationsīy default, the array methods in JavaScript will mutate your array. Here's a way to remove an array element without mutating the array.
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