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


npm i python-range


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]


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


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])

Executes the callback once for each element with element, current index and the range as arguments. Works the same as Array.prototype.forEach().

PythonRange.prototype.includes(<int> value)

Returns true if the range contains the specified value; otherwise returns false.

console.log(range(3, 5).includes(3)); // true
console.log(range(10).includes(10)); // false


Returns the smallest value in the range.

console.log(range(10).min()); // 0
console.log(range(0, -15, -1).min()); // -14


Returns the largest value in the range.

console.log(range(10).max()); // 9
console.log(range(12, 0, -2).max()); // 12


Reverses the range in-place and returns it.

console.log(range(2, 5).reverse()); // range(4, 1, -1)
console.log(range(10, 0, -1).reverse()); // range(1, 11, 1)


Returns a string range(<start>, <stop>, <step>), where <start>, <stop> and <step> are the start, stop and step properties of the range.

console.log(String(range(3, 6, 2))); // range(3, 6, 2)


Returns the result of the toString() method.


Returns the result of calling Array.prototype.values() on the range.

PythonRange.areEqual(<PythonRange> a, <PythonRange> b)

Returns true if the passed arguments are equal; otherwise returns false. Two ranges are considered equals if they contain the same set of values. For example, range(3, 3) and range(0) are equal, because they're both empty ranges. range(4, 5, 2) and range(4, 6, 3) are equal too, because they both contain only one element: 4.

const r = range(3);
console.log(PythonRange.areEqual(r, r)); // true
console.log(PythonRange.areEqual(range(10), range(10))); // true
console.log(PythonRange.areEqual(range(3, 3), range(0))); // true, because both ranges are empty
console.log(PythonRange.areEqual(range(4, 5, 2), range(4, 6, 3))); // true, because both ranges contain only one element: 4
console.log(PythonRange.areEqual(range(2), range(3))); // false


Returns an instance of PythonRange with the specified arguments.

Supported environments

In order to be able to access numeric properties (e.g. r[2]), native Proxy support is required (see compatibility table). If you want to execute your code in environments without Proxy support, you can use the get() method instead.


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








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