docs.sheetjs.com/docz/docs/03-demos/12-engines/index.md

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title: JavaScript Engines
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Browser vendors and other organizations have built "JavaScript engines".  They
are independent software libraries that are capable of running JS scripts.

The most popular JavaScript engine is V8.  Designed for embedding in software,
it powers Chrome, NodeJS, UXP, Deno and many other platforms.

There are many other JS engines with different design goals.  Some are designed
for low-power or low-memory environments.  Others aim for interoperability with
specific programming languages or environments.  Typically they support ES3 and
are capable of running SheetJS code.

This demo showcases a number of JS engines and language bindings.

## General Caveats

Common browser and NodeJS APIs are often missing from light-weight JS engines.

**Global**

Some engines do not provide `globalThis` or `global` or `window`.  A `global`
variable can be exposed in one line that should be run in the JS engine:

```js
var global = (function(){ return this; }).call(null);
```

**Console**

Some engines do not provide a `console` object.  `console.log` can be shimmed
using the engine functionality.  For example, `hermes`[^1] provides `print()`:

```js
var console = { log: function(x) { print(x); } };
```

**Binary Data**

Some engines do not provide easy ways to exchange binary data.  For example, it
is common to pass null-terminated arrays, which would truncate XLSX, XLS, and
other exports.  APIs that accept pointers without length should be avoided.

Base64 strings are safe for passing between JS and native code, but they should
only be used when there is no safe way to pass `ArrayBuffer` or `Uint8Array`.

**Byte Conventions**

Java has no native concept of unsigned bytes. Values in a `byte[]` are clamped
to the range `-128 .. 127`. They need to be fixed within the JS engine.

Some engines support typed arrays. The `Uint8Array` constructor will fix values:

```js
var signed_data = [-48, -49, 17, -32, /* ... */]; // 0xD0 0xCF 0x11 0xE0 ...
var fixed_data = new Uint8Array(signed_data);
```

When `Uint8Array` is not supported, values can be fixed with bitwise operations:

```js
var signed_data = [-48, -49, 17, -32, /* ... */]; // 0xD0 0xCF 0x11 0xE0 ...
var fixed_data = new Array(signed_data.length);
for(var i = 0; i < signed_data.length; ++i) fixed_data[i] = signed_data[i] & 0xFF;
```

## Engines

This list is sorted in alphabetical order.

### Boa

Boa is an embeddable JS engine written in Rust.

This demo has been moved [to a dedicated page](/docs/demos/engines/boa).

### ChakraCore

ChakraCore is an embeddable JS engine written in C++.

This demo has been moved [to a dedicated page](/docs/demos/engines/chakra).

### Duktape

Duktape is an embeddable JS engine written in C. It has been ported to a number
of exotic architectures and operating systems.

This demo has been moved [to a dedicated page](/docs/demos/engines/duktape).
The demo includes examples in C and Perl.

### Goja

Goja is a pure Go implementation of ECMAScript 5.

This demo has been moved [to a dedicated page](/docs/demos/engines/goja).

### Hermes

Hermes is an embeddable JS engine written in C++.

This demo has been moved [to a dedicated page](/docs/demos/engines/hermes).

### JavaScriptCore

iOS and MacOS ship with the JavaScriptCore framework for running JS code from
Swift and Objective-C.

This demo has been moved [to a dedicated page](/docs/demos/engines/jsc).


### JerryScript

JerryScript is a lightweight JavaScript engine designed for use in low-memory
environments like microcontrollers.  As part of the build suite, the project
generates a C library and a standalone CLI tool.

The simplest way to interact with the engine is to pass Base64 strings.

:::note

While applications should link against the official libraries, the standalone tool
is useful for verifying functionality.

:::

:::caution

This demo requires a much larger heap size than is normally used in JerryScript
deployments! In local testing, the following sizes were needed:

- 8192 (8M) for <https://sheetjs.com/pres.xlsx>
- 65536 (64M) for <https://sheetjs.com/pres.numbers>

This works on a Raspberry Pi.

:::

<details><summary><b>Complete Example</b> (click to show)</summary>

Due to limitations of the standalone binary, this demo will encode a test file
as a Base64 string and directly add it to an amalgamated script.

0) Build the library and command line tool with required options:

```bash
git clone --depth=1 https://github.com/jerryscript-project/jerryscript.git
cd jerryscript
python tools/build.py --error-messages=ON --logging=ON --mem-heap=8192 --cpointer-32bit=ON
```

1) Download the standalone script, shim, and test file:

<ul>
<li><a href={`https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js`}>xlsx.full.min.js</a></li>
<li><a href={`https://cdn.sheetjs.com/xlsx-${current}/package/dist/shim.min.js`}>shim.min.js</a></li>
<li><a href="https://sheetjs.com/pres.xlsx">pres.xlsx</a></li>
</ul>

2) Bundle the test file and create `payload.js`:

```bash
node -e "fs.writeFileSync('payload.js', 'var payload = \"' + fs.readFileSync('pres.xlsx').toString('base64') + '\";')"
```

3) Create support scripts:

- `global.js` creates a `global` variable and defines a fake `console`:

```js title="global.js"
var global = (function(){ return this; }).call(null);
var console = { log: function(x) { print(x); } };
```

- `jerry.js` will call `XLSX.read` and `XLSX.utils.sheet_to_csv`:

```js title="jerry.js"
/* sheetjs (C) 2013-present  SheetJS -- https://sheetjs.com */
var wb = XLSX.read(payload, {type:'base64'});
console.log(XLSX.utils.sheet_to_csv(wb.Sheets[wb.SheetNames[0]]));
```

4) Create the amalgamation `xlsx.jerry.js`:

```bash
cat global.js xlsx.full.min.js payload.js jerry.js > xlsx.jerry.js
```

The final script defines `global` before loading the standalone library.  Once
ready, it will read the bundled test data and print the contents as CSV.

5) Run the script using the `jerry` standalone binary:

```bash
build/bin/jerry xlsx.jerry.js; echo $?
```

</details>


### Nashorn

Nashorn shipped with some versions of Java.  It is now a standalone library.

This demo has been moved [to a dedicated page](/docs/demos/engines/nashorn).


### QuickJS

QuickJS is an embeddable JS engine written in C.  It provides a separate set of
functions for interacting with the filesystem and the global object.  It can run
the standalone browser scripts.

This demo has been moved [to a dedicated page](/docs/demos/engines/quickjs).


### Rhino

Rhino is an ES3+ engine in Java.

This demo has been moved [to a dedicated page](/docs/demos/engines/rhino).


### V8

V8 is an embeddable JS engine written in C++. It powers Chromium and Chrome,
NodeJS and Deno, Adobe UXP and other platforms.

This demo has been moved [to a dedicated page](/docs/demos/engines/v8).
The demo includes examples in C++ and Rust.

The ["Python + Pandas" demo](/docs/demos/engines/pandas) uses V8 with Python.

[^1]: See ["Initialize Hermes"](/docs/demos/engines/hermes#initialize-hermes) in the Hermes demo.