29th February, 2020

Python-style list slicing in JavaScript


View source code on GitHub

Build: adamauckland

View all the tests

Do you love Python list slicing?

Want to do this..

items = ["apple", "ball", "cat"]

items[-1:] # returns ["cat]

items[-1] # returns "cat"

items[:1] # returns ["apple"]

Then this module is for you!


Create an array:

const array = [

Create a PyJsArray object, passing your array in:

const newArray = new PyJsArray(array);

Accessing from the end backwards:

newArray[-1] // returns "dog"

PyJsArray also accepts the start:end format, which must be quoted or JS will think it's an object

newArray["-2:"] // returns ["cat", "dog"]

Stepped slicing

Stepped slicing. A third "step" parameter can be passed in to return every 2nd, 3rd or nth item. It also works in reverse.

const array = [

newArray["1:5:2"] // returns ["ball", "dog" ]

When reversing, start index must be higher than end index.


In the above example, we do not get "fish" returned because "fish" is at index[5] and as 5 is our end index (non-inclusive), it gets ommitted.

That's how it works in Python.

Javascript uses : so when you want to use : QUOTE IT! sorry.


The opinions expressed here are my own and not those of my employer.