docs.sheetjs.com/docz/docs/03-demos/42-engines/index.md

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---
title: JavaScript Engines
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pagination_prev: demos/bigdata/index
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---
import current from '/version.js';
import Tabs from '@theme/Tabs';
import TabItem from '@theme/TabItem';
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import CodeBlock from '@theme/CodeBlock';
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import EngineData from '/data/engines.js'
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[SheetJS](https://sheetjs.com) is a JavaScript library for reading and writing
data from spreadsheets.
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JavaScript code cannot be directly executed on most modern computers. A software
component ("JavaScript engine") executes code. There are many engines designed
for embedding in other applications. After embedding a JS engine in software,
programs can leverage SheetJS libraries to process spreadsheets and data.
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The demos in this section showcase a number of JS engines and language bindings.
In each case, we will build a sample application that embeds a JS engine, loads
SheetJS library scripts, and reads and writes spreadsheet files.
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## General Caveats
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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.
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Common browser and NodeJS APIs are often missing from light-weight JS engines.
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#### Global
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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);
```
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#### Console
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Some engines do not provide a `console` object but offer other ways to print to
standard output. For example, Hermes[^1] provides `print()`. A `console` object
should be created using the engine print function:
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```js
var console = { log: function(x) { print(x); } };
```
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#### Binary Data
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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.
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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`.
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#### Byte Conventions
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Java has no native concept of unsigned bytes. Values in a `byte[]` are limited
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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;
```
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## Engines
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:::info pass
Demos are tested across multiple operating systems (Windows, MacOS and Linux)
across multiple architectures (x64 and ARM64).
:::
<EngineData/>
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#### Boa
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Boa is an embeddable JS engine written in Rust.
This demo has been moved [to a dedicated page](/docs/demos/engines/boa).
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#### ChakraCore
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ChakraCore is an embeddable JS engine written in C++.
This demo has been moved [to a dedicated page](/docs/demos/engines/chakra).
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#### Duktape
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Duktape is an embeddable JS engine written in C. It has been ported to a number
of exotic architectures and operating systems.
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This demo has been moved [to a dedicated page](/docs/demos/engines/duktape).
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The demo includes examples in C, Perl, PHP, Python and Zig.
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#### Goja
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Goja is a pure Go implementation of ECMAScript 5.
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This demo has been moved [to a dedicated page](/docs/demos/engines/goja).
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#### Hermes
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Hermes is an embeddable JS engine written in C++.
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This demo has been moved [to a dedicated page](/docs/demos/engines/hermes).
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#### JavaScriptCore
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iOS and MacOS ship with the JavaScriptCore framework for running JS code from
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Swift and Objective-C.
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This demo has been moved [to a dedicated page](/docs/demos/engines/jsc).
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#### JerryScript
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JerryScript is a lightweight JavaScript engine designed for use in low-memory
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environments including microcontrollers.
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This demo has been moved [to a dedicated page](/docs/demos/engines/jerryscript).
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#### Jint
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Jint is an embeddable JS engine for .NET written in C#.
This demo has been moved [to a dedicated page](/docs/demos/engines/jint).
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#### Nashorn
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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).
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#### QuickJS
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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.
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This demo has been moved [to a dedicated page](/docs/demos/engines/quickjs).
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#### Rhino
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Rhino is an ES3+ engine in Java.
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This demo has been moved [to a dedicated page](/docs/demos/engines/rhino).
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#### V8
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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.
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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.