How to Create Python range() in JavaScript

Use the beloved Python range() operator in JavaScript via Iterators

Photo by Yudi Silvercloud on Unsplash

What is the Python range() type?

If you’re not familiar with Python, range() refers to the use of the range type to create an immutable sequence of numbers.

“The range type represents an immutable sequence of numbers and is commonly used for looping a specific number of times in for loops.” — docs.python.org

The range() constructor has two forms of definition:

range(stop)
range(start, stop[, step])

A concise explanation of the parameters, return value, etc. can be found on programiz.

A few examples:

Building the range() function in JavaScript

For simplicity sake, we will ignore the optional step argument.

By using the Array constructor, fill and map, you could work out a simple solution in a quick one-liner:

new Array(stop - start).fill(start).map((el, i) => el + i)

And maybe then offer a more complete solution, covering the case of calling range with only one argument:

But it’s not quite it yet. Can you see why this solution is wrong?

Remember, calling Python range returns an immutable sequence of numbers. Notice how in order to get the familiar list data structure, the Python examples above wrap the return value of range with list().

An equal example in JavaScript should probably look something like this: