JavaScript Engines

SheetJS is a JavaScript library for reading and writing data from spreadsheets.

JavaScript code cannot be directly executed on most modern computers. A software component ("JavaScript engine") executes code. After embedding a JS engine, programs can leverage SheetJS libraries to process spreadsheets and data.

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.

General Caveats

There are many 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.

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:

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

Console

Some engines do not provide a console object but offer other ways to print to standard output. For example, Hermes¹ provides print(). A console object should be created using the engine print function:

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

Binary Data

Some engines do not provide easy ways to exchange binary data. For example, some libraries 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, as they do not use null characters, but should only be used when there is no safe way to pass ArrayBuffer or Uint8Array objects. The SheetJS read² and write³ methods directly support Base64 strings.

Byte Conventions

Java has no native concept of unsigned bytes. Values in a byte[] are limited 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:

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:

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

Demos are tested across multiple operating systems (Windows, MacOS and Linux) across multiple architectures (x64 and ARM64).

The following engines have been tested in their native languages:

The following bindings have been tested:

Asterisks (✱) in the Windows columns mark tests that were run in Windows Subsystem for Linux (WSL)

Boa

Boa is an embeddable JS engine written in Rust.

This demo has been moved to a dedicated page.

ChakraCore

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

This demo has been moved to a dedicated page.

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. The demo includes examples in C, Perl, PHP, Python and Zig.

Goja

Goja is a pure Go implementation of ECMAScript 5.

This demo has been moved to a dedicated page.

Hermes

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

This demo has been moved to a dedicated page.

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.

JerryScript

JerryScript is a lightweight JavaScript engine designed for use in low-memory environments including microcontrollers.

This demo has been moved to a dedicated page.

Jint

Jint is an embeddable JS engine for .NET written in C#.

This demo has been moved to a dedicated page.

Nashorn

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

This demo has been moved to a dedicated page.

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.

Rhino

Rhino is an ES3+ engine in Java.

This demo has been moved to a dedicated page.

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. The demo includes examples in C++ and Rust.

The "Python + Pandas" demo uses V8 with Python.

Footnotes

1. See "Initialize Hermes" in the Hermes demo. ↩

2. See read in "Reading Files" ↩

3. See write in "Writing Files" ↩