https://github.com/Rich-Harris/vlq

Generate, and decode, base64 VLQ mappings for sourcemaps and other uses
https://github.com/Rich-Harris/vlq

Last synced: 9 days ago
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Generate, and decode, base64 VLQ mappings for sourcemaps and other uses

• Host: GitHub
• URL: https://github.com/Rich-Harris/vlq
• Owner: Rich-Harris
• License: mit
• Created: 2014-09-28T19:07:31.000Z (over 9 years ago)
• Default Branch: master
• Last Pushed: 2023-09-18T09:45:00.000Z (9 months ago)
• Last Synced: 2024-05-16T03:49:21.259Z (about 1 month ago)
• Language: JavaScript
• Homepage:
• Size: 293 KB
• Stars: 200
• Watchers: 7
• Forks: 18
• Open Issues: 3
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGELOG.md
  • License: LICENSE

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• awesome-github-star - vlq - Harris | 188 | (JavaScript)

README

        
# vlq.js

Convert integers to a Base64-encoded VLQ string, and vice versa. No dependencies, works in node.js or browsers, supports AMD.

## Why would you want to do that?

Sourcemaps are the most likely use case. Mappings from original source to generated content are encoded as a sequence of VLQ strings.

## What is a VLQ string?

A [variable-length quantity](http://en.wikipedia.org/wiki/Variable-length_quantity) is a compact way of encoding large integers in text (i.e. in situations where you can't transmit raw binary data). An integer represented as digits will always take up more space than the equivalent VLQ representation:

| Integer             | VLQ        |

| :------------------ | :--------- |

| 0                   | A          |

| 1                   | C          |

| -1                  | D          |

| 123                 | 2H         |

| 123456789           | qxmvrH     |

## Installation

```bash

npm install vlq

```

## Usage

### Encoding

`vlq.encode` accepts an integer, or an array of integers, and returns a string:

```js

vlq.encode(123); // '2H';

vlq.encode([123, 456, 789]); // '2HwcqxB'

```

### Decoding

`vlq.decode` accepts a string and always returns an array:

```js

vlq.decode('2H'); // [123]

vlq.decode('2HwcqxB'); // [123, 456, 789]

```

## Limitations

Since JavaScript bitwise operators work on 32 bit integers, the maximum value this library can handle is 2^30 - 1, or 1073741823.

## Using vlq.js with sourcemaps

[See here for an example of using vlq.js with sourcemaps.](https://github.com/Rich-Harris/vlq/tree/master/sourcemaps)

## Credits

Adapted from [murzwin.com/base64vlq.html](http://murzwin.com/base64vlq.html) by Alexander Pavlov.

## License

[MIT](LICENSE).