A JavaScript implementation of the Python's range() function.

Installation

npm i python-range

Examples

Try it out in your browser.

Basic usage

import range from 'python-range';
const r = range(10);
console.log(r); // range(0, 10, 1)
console.log(Array.from(r)); // [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
console.log(r[3]); // 3
console.log(r.length); // 10
console.log(Array.from(range(2, 5))); // [2, 3, 4]
console.log(Array.from(range(5, 0, -1))); // [5, 4, 3, 2, 1]

Iteration

const r = range(3, 6);
for (const n of r) {
  console.log(n); // logs 3, 4 and 5
}
r.forEach(n => console.log(n)); // logs 3, 4, and 5

Lazy evaluation

Unlike other range modules, python-range has lazy evaluation.

See Why is “1000000000000000 in range(1000000000000001)” so fast in Python 3?

console.log(range(1000000000000001).includes(1000000000000000)); // true
console.log(range(0, 100000000000001, 10).includes(100000000000000)); // true
console.log(range(0, -1000000000, -3)[12345678]); // -37037034

Documentation

Exported values

python-range exports two values: a PythonRange class, and a range function (a default export), which returns a PythonRange object.

import range, {PythonRange} from 'python-range';
console.log(range(10) instanceof PythonRange); // true

new PythonRange(<int> start, <int> stop[, <int> step])

The PythonRange constructor creates a range starting with start (inclusive) and ending with stop (exclusive). The step parameter defaults to 1 and specifies the distance between two elements. The step parameter must be different than 0.

new PythonRange(<int> stop)

When called with only one argument, the start parameter defaults to 0 and the passed argument becomes stop.

const r = range(3);
console.log(r.start); // 0
console.log(r.stop); // 3

Numeric properties

You can access range elements using array indices. Note that this requires native Proxy support.

const r = range(2, 5);
console.log(r[0]); // 2
console.log(r[2]); // 4

start, stop and step properties

The PythonRange constructor creates these properties based on the arguments passed to the constructor, or the default values. These properties are writable, and changing them automatically updates the range.

const r = range(5);
console.log(Array.from(r)); // [0, 1, 2, 3, 4]
r.step = 2;
console.log(Array.from(r)); // [0, 2, 4]

length property

The length property specifies the number of elements in the range. It's updated automatically when the start, stop and step properties are changed.

const r = range(5);
console.log(r.length); // 5
r.stop = 3;
console.log(r.length); // 3

PythonRange.prototype.get(<int> index)

Works the same as accessing numeric properties (e.g. r[2]). Use this method if you want to execute your code in environments without native Proxy support.

console.log(range(2, 5).get(1)); // 3

PythonRange.prototype.forEach(<callable> callback[, <object> thisArg])