The final element's index is -1, the next-to-last element's index is -2, and so on.Ĭonst languages = You may also use negative start and end indices with JavaScript. log(new_arr2) // Įxample 2: Negative index slice() in JavaScript slicing from the second element to fourth elementĬonsole. ExamplesĮxample 1: The slice() function in JavaScript. Returns a new array that contains the elements that were removed. The selection stops at the final element's index if it is not given. end (optional) - The selection's final index (exclusive).Unless otherwise specified, the selection begins at start 0. start (optional) - The selection's initial index.

For more Javascript, check out my other articles here.The slice() method's syntax is as follows:

Javascript slice copies still have the same reference as the original in memory, which is useful to know when manipulating them. It can also be used in a limited way to make duplicates that can be independently updated. The Javascript slice method is useful for creating new shallow copies of arrays with a subset of the original arrays data. Knowing this little piece of trivia is going to save you a lot of time someday. That means that although it may seem like you are making a copy with slice when working with simple arrays, this does not hold up when using it on more complex objects.

However, somewhat confusingly, by using the arrayOneSlice notation, Javascript interprets this as putting a new value into the place of the shallow copy itself. In the first example, using the ems notation, Javascript interprets this as updating an existing element within the shallow copy and thus it affects the original. Wait, what? We changed arrayOneSlice’s items object, but its changed in both arrayOne and arrayOneSlice! Meanwhile, arrayOneSlice has only changed arrayOneSlice! Welcome to another Javascript quirk.

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