# v8-compile-cache-lib

> Fork of [`v8-compile-cache`](https://www.npmjs.com/package/v8-compile-cache) exposed as an API for programmatic usage in other libraries and tools.

***

[![Build status](https://img.shields.io/github/workflow/status/cspotcode/v8-compile-cache-lib/Continuous%20Integration)](https://github.com/cspotcode/v8-compile-cache-lib/actions?query=workflow%3A%22Continuous+Integration%22)

`v8-compile-cache-lib` attaches a `require` hook to use [V8's code cache](https://v8project.blogspot.com/2015/07/code-caching.html) to speed up instantiation time. The "code cache" is the work of parsing and compiling done by V8.

The ability to tap into V8 to produce/consume this cache was introduced in [Node v5.7.0](https://nodejs.org/en/blog/release/v5.7.0/).

## Usage

1. Add the dependency:

```sh
$ npm install --save v8-compile-cache-lib
```

2. Then, in your entry module add:

```js
require('v8-compile-cache-lib').install();
```

**`.install()` in Node <5.7.0 is a noop – but you need at least Node 4.0.0 to support the ES2015 syntax used by `v8-compile-cache-lib`.**

## Options

Set the environment variable `DISABLE_V8_COMPILE_CACHE=1` to disable the cache.

Cache directory is defined by environment variable `V8_COMPILE_CACHE_CACHE_DIR` or defaults to `<os.tmpdir()>/v8-compile-cache-<V8_VERSION>`.

## Internals

Cache files are suffixed `.BLOB` and `.MAP` corresponding to the entry module that required `v8-compile-cache-lib`. The cache is *entry module specific* because it is faster to load the entire code cache into memory at once, than it is to read it from disk on a file-by-file basis.

## Benchmarks

See <https://github.com/cspotcode/v8-compile-cache-lib/tree/master/bench>.

**Load Times:**

| Module           | Without Cache | With Cache |
| ---------------- | ------------: | ---------: |
| `babel-core`     |       `218ms` |    `185ms` |
| `yarn`           |       `153ms` |    `113ms` |
| `yarn` (bundled) |       `228ms` |    `105ms` |

*^ Includes the overhead of loading the cache itself.*

## Acknowledgements

* The original [`v8-compile-cache`](https://github.com/zertosh/v8-compile-cache) from which this library is forked.
* `FileSystemBlobStore` and `NativeCompileCache` are based on Atom's implementation of their v8 compile cache:
  * <https://github.com/atom/atom/blob/b0d7a8a/src/file-system-blob-store.js>
  * <https://github.com/atom/atom/blob/b0d7a8a/src/native-compile-cache.js>
* `mkdirpSync` is based on:
  * <https://github.com/substack/node-mkdirp/blob/f2003bb/index.js#L55-L98>


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