Skip to main content

JavaScript Engines

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.

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:

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 provides print():

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.

Duktape

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

Reading data

Duktape supports Buffer natively but should be sliced before processing:

/* parse a C char array as a workbook object */
duk_push_external_buffer(ctx);
duk_config_buffer(ctx, -1, buf, len);
duk_put_global_string(ctx, "buf");
duk_eval_string_noresult("workbook = XLSX.read(buf.slice(0, buf.length), {type:'buffer'});");

Writing data

duk_get_buffer_data can pull Buffer object data into the C code:

/* write a workbook object to a C char array */
duk_eval_string(ctx, "XLSX.write(workbook, {type:'array', bookType:'xlsx'})");
duk_size_t sz;
char *buf = (char *)duk_get_buffer_data(ctx, -1, sz);
duk_pop(ctx);
Complete Example (click to show)
note

This demo was tested on Intel Mac (darwin-x64).

0) Download and extract the latest release (2.7.0 at the time of writing)

curl -LO https://duktape.org/duktape-2.7.0.tar.xz
tar -xJf duktape-2.7.0.tar.xz
mv duktape-2.7.0/src/*.{c,h} .

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

2) Save the following script to sheetjs.duk.c:

sheetjs.duk.c
/* sheetjs (C) 2013-present  SheetJS -- http://sheetjs.com */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "duktape.h"

#define FAIL_LOAD { \
duk_push_undefined(ctx); \
perror("Error in load_file"); \
return 1; \
}

static char *read_file(const char *filename, size_t *sz) {
FILE *f = fopen(filename, "rb");
if(!f) return NULL;
long fsize; { fseek(f, 0, SEEK_END); fsize = ftell(f); fseek(f, 0, SEEK_SET); }
char *buf = (char *)malloc(fsize * sizeof(char));
*sz = fread((void *) buf, 1, fsize, f);
fclose(f);
return buf;
}

static duk_int_t eval_file(duk_context *ctx, const char *filename) {
size_t len; char *buf = read_file(filename, &len);
if(!buf) FAIL_LOAD

duk_push_lstring(ctx, (const char *)buf, (duk_size_t)len);
duk_int_t retval = duk_peval(ctx);
duk_pop(ctx);
return retval;
}

static duk_int_t load_file(duk_context *ctx, const char *filename, const char *var) {
size_t len; char *buf = read_file(filename, &len);
if(!buf) FAIL_LOAD

duk_push_external_buffer(ctx);
duk_config_buffer(ctx, -1, buf, len);
duk_put_global_string(ctx, var);
return 0;
}

static duk_int_t save_file(duk_context *ctx, const char *filename, const char *var) {
duk_get_global_string(ctx, var);
duk_size_t sz;
char *buf = (char *)duk_get_buffer_data(ctx, -1, &sz);

if(!buf) return 1;
FILE *f = fopen(filename, "wb"); fwrite(buf, 1, sz, f); fclose(f);
return 0;
}

#define FAIL(cmd) { \
printf("error in %s: %s\n", cmd, duk_safe_to_string(ctx, -1)); \
duk_destroy_heap(ctx); \
return res; \
}

#define DOIT(cmd) duk_eval_string_noresult(ctx, cmd);
int main(int argc, char *argv[]) {
duk_int_t res = 0;

/* initialize */
duk_context *ctx = duk_create_heap_default();
/* duktape does not expose a standard "global" by default */
DOIT("var global = (function(){ return this; }).call(null);");

/* load library */
res = eval_file(ctx, "shim.min.js");
if(res != 0) FAIL("shim load")
res = eval_file(ctx, "xlsx.full.min.js");
if(res != 0) FAIL("library load")

/* get version string */
duk_eval_string(ctx, "XLSX.version");
printf("SheetJS library version %s\n", duk_get_string(ctx, -1));
duk_pop(ctx);

/* read file */
res = load_file(ctx, argv[1], "buf");
if(res != 0) FAIL("file load")
printf("Loaded file %s\n", argv[1]);

/* parse workbook */
DOIT("wb = XLSX.read(buf.slice(0, buf.length), {type:'buffer'});");
DOIT("ws = wb.Sheets[wb.SheetNames[0]]");

/* print CSV */
duk_eval_string(ctx, "XLSX.utils.sheet_to_csv(ws)");
printf("%s\n", duk_get_string(ctx, -1));
duk_pop(ctx);

/* write file */
#define WRITE_TYPE(BOOKTYPE) \
DOIT("newbuf = (XLSX.write(wb, {type:'array', bookType:'" BOOKTYPE "'}));");\
res = save_file(ctx, "sheetjsw." BOOKTYPE, "newbuf");\
if(res != 0) FAIL("save sheetjsw." BOOKTYPE)

WRITE_TYPE("xlsb")

/* cleanup */
duk_destroy_heap(ctx);
return res;
}

3) Compile standalone sheetjs.duk binary

gcc -std=c99 -Wall -osheetjs.duk sheetjs.duk.c duktape.c -lm

4) Run the demo:

./sheetjs.duk pres.numbers

If the program succeeded, the CSV contents will be printed to console and the file sheetjsw.xlsb will be created. That file can be opened with Excel.

Goja

Goja is a pure Go implementation of ECMAScript 5. It supports the standalone scripts out of the box.

Reading data

Files can be read into []byte:

/* read file */
data, _ := ioutil.ReadFile("sheetjs.xlsx")

[]byte should be converted to an ArrayBuffer from Go:

/* load into engine */
vm.Set("buf", vm.ToValue(vm.NewArrayBuffer(data)))

/* parse */
wb, _ = vm.RunString("wb = XLSX.read(buf, {type:'buffer'});")

Writing data

"base64" strings can be decoded in Go:

/* write to Base64 string */
b64str, _ := vm.RunString("XLSX.write(wb, {type:'base64', bookType:'xlsx'})")

/* pull data back into Go and write to file */
buf, _ := base64.StdEncoding.DecodeString(b64str.String())
_ = ioutil.WriteFile("sheetjs.xlsx", buf, 0644)
Complete Example (click to show)

0) Install Go

1) Create a go.mod file and install dependencies:

go mod init SheetGoja
go get github.com/dop251/goja

2) Download the standalone script and the shim:

3) Save the following code to SheetGoja.go:

SheetGoja.go
package main

import (
b64 "encoding/base64"
"fmt"
"os"
"io/ioutil"
"github.com/dop251/goja"
)

func safe_run_file(vm *goja.Runtime, file string) {
data, err := ioutil.ReadFile(file)
if err != nil { panic(err) }
src := string(data)
_, err = vm.RunString(src)
if err != nil { panic(err) }
}

func eval_string(vm *goja.Runtime, cmd string) goja.Value {
v, err := vm.RunString(cmd)
if err != nil { panic(err) }
return v
}

func write_type(vm *goja.Runtime, t string) {
b64str := eval_string(vm, "XLSX.write(wb, {type:'base64', bookType:'" + t + "'})")
buf, err := b64.StdEncoding.DecodeString(b64str.String());
if err != nil { panic(err) }
err = ioutil.WriteFile("sheetjsg." + t, buf, 0644)
if err != nil { panic(err) }
}

func main() {
vm := goja.New()

/* initialize */
eval_string(vm, "if(typeof global == 'undefined') global = (function(){ return this; }).call(null);")

/* load library */
safe_run_file(vm, "shim.min.js")
safe_run_file(vm, "xlsx.full.min.js")

/* get version string */
v := eval_string(vm, "XLSX.version")
fmt.Printf("SheetJS library version %s\n", v)

/* read file */
data, err := ioutil.ReadFile(os.Args[1])
if err != nil { panic(err) }
vm.Set("buf", vm.ToValue(vm.NewArrayBuffer(data)))
fmt.Printf("Loaded file %s\n", os.Args[1])

/* parse workbook */
eval_string(vm, "wb = XLSX.read(buf, {type:'buffer'});")
fmt.Printf("Parsed %s\n", os.Args[1])
eval_string(vm, "ws = wb.Sheets[wb.SheetNames[0]]")
fmt.Printf("Grabbed %s\n", os.Args[1])

/* print CSV */
csv := eval_string(vm, "XLSX.utils.sheet_to_csv(ws)")
fmt.Printf("%s\n", csv)

/* write file */
write_type(vm, "csv")
}

4) Build SheetGoja:

go build SheetGoja.go

For testing, download https://sheetjs.com/pres.numbers and run

./SheetGoja pres.numbers

This will print the contents as a CSV to screen AND write to sheetjsg.csv

Hermes

Hermes is an embeddable JS engine for React Native. The library and binary distributions include a command-line tool hermes for running JS scripts.

The simplest way to interact with the engine is to pass Base64 strings. The make target builds a very simple payload with the data.

note

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

Complete Example (click to show)

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) Install the hermes command line tool

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

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

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

3) Create support scripts:

  • global.js creates a global variable and defines a fake console:
global.js
var global = (function(){ return this; }).call(null);
var console = { log: function(x) { print(x); } };
  • hermes.js will call XLSX.read and XLSX.utils.sheet_to_csv:
hermes.js
/* sheetjs (C) 2013-present  SheetJS -- http://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.hermes.js:

cat global.js xlsx.full.min.js payload.js hermes.js > xlsx.hermes.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 Hermes standalone binary:

hermes xlsx.hermes.js

JavaScriptCore

Platform Limitations

JavaScriptCore is primarily deployed in MacOS and iOS applications. There is some experimental support through the Bun runtime, but production applications intending to support Windows / Linux / Android should try to embed V8.

iOS and MacOS ship with the JavaScriptCore framework for running JS code from Swift and Objective-C. Hybrid function invocation is tricky, but explicit data passing is straightforward. The demo shows a standalone Swift sample for MacOS.

Binary strings can be passed back and forth using String.Encoding.isoLatin1.

Reading data

String(contentsOf:encoding:) reads from a path and returns an encoded string:

/* read sheetjs.xls as Base64 string */
let file_path = shared_dir.appendingPathComponent("sheetjs.xls");
let data: String! = try String(contentsOf: file_path, encoding: String.Encoding.isoLatin1);

This string can be loaded into the JS engine and processed:

/* load data in JSC */
context.setObject(data, forKeyedSubscript: "payload" as (NSCopying & NSObjectProtocol));

/* `payload` (the "forKeyedSubscript" parameter) is a binary string */
context.evaluateScript("var wb = XLSX.read(payload, {type:'binary'});");

Writing data

When writing to binary string in JavaScriptCore, the result should be stored in a variable and converted to string in Swift:

/* write to binary string */
context.evaluateScript("var out = XLSX.write(wb, {type:'binary', bookType:'xlsx'})");

/* `out` from the script is a binary string that can be stringified in Swift */
let outvalue: JSValue! = context.objectForKeyedSubscript("out");
var out: String! = outvalue.toString();

String#write(to:atomically:encoding) writes the string to the specified path:

/* write to sheetjsw.xlsx */
let out_path = shared_dir.appendingPathComponent("sheetjsw.xlsx");
try? out.write(to: out_path, atomically: false, encoding: String.Encoding.isoLatin1);

The demo includes a sample SheetJSCore Wrapper class to simplify operations.

Complete Example (click to show)
This demo only runs on MacOS

This example requires MacOS + Swift and will not work on Windows or Linux!

0) Ensure Xcode is installed

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

2) Download the Swift scripts for the demo

3) Build the SheetJSwift binary:

swiftc SheetJSCore.swift main.swift -o SheetJSwift

4) Test the program:

./SheetJSwift pres.numbers

If successful, a CSV will be printed to console. The script also tries to write to SheetJSwift.xlsx. That file can be verified by opening in Excel / Numbers.

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:

This works on a Raspberry Pi.

Complete Example (click to show)

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:

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:

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

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:
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:
jerry.js
/* sheetjs (C) 2013-present  SheetJS -- http://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:

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:

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

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.

Complete Example (click to show)

0) Ensure quickjs command line utility is installed

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

2) Save the following script to SheetJSQuick.js:

"SheetJSQuick.js
/* sheetjs (C) 2013-present  SheetJS -- http://sheetjs.com */
/* load XLSX */
import * as std from "std";
globalThis.global = globalThis;
std.loadScript("xlsx.full.min.js");

/* read contents of file */
var rh = std.open("pres.numbers", "rb");
rh.seek(0, std.SEEK_END);
var sz = rh.tell();
var ab = new ArrayBuffer(sz);
rh.seek();
rh.read(ab, 0, sz);
rh.close();

/* parse file */
var wb = XLSX.read(ab, {type: 'array'});

/* write array */
var out = XLSX.write(wb, {type: 'array'});

/* write contents to file */
var wh = std.open("SheetJSQuick.xlsx", "wb");
wh.write(out, 0, out.byteLength);
wh.close();

3) Test the program:

quickjs SheetJSQuick.js

If successful, the script will generate SheetJSQuick.xlsx.

Rhino

Rhino is an ES3+ engine in Java. The SheetJSRhino class and com.sheetjs package show a complete JAR deployment, including the full XLSX source.

Due to code generation errors, optimization must be turned off:

Context context = Context.enter();
context.setOptimizationLevel(-1);
Complete Example (click to show)

0) Download the appropriate Rhino build and rename to rhino.jar

1) Download SheetJSRhino.zip and unzip

2) Save the following code to SheetJSRhino.java:

SheetJSRhino.java
/* sheetjs (C) 2013-present  SheetJS -- http://sheetjs.com */
/* vim: set ts=2: */
import com.sheetjs.SheetJS;
import com.sheetjs.SheetJSFile;
import com.sheetjs.SheetJSSheet;

public class SheetJSRhino {
public static void main(String args[]) throws Exception {
try {
SheetJS sjs = new SheetJS();

/* open file */
SheetJSFile xl = sjs.read_file(args[0]);

/* get sheetnames */
String[] sheetnames = xl.get_sheet_names();
System.err.println(sheetnames[0]);

/* convert to CSV */
SheetJSSheet sheet = xl.get_sheet(0);
String csv = sheet.get_csv();

System.out.println(csv);

} catch(Exception e) {
throw e;
} finally {
SheetJS.close();
}
}
}

3) Assemble SheetJS.jar from the demo code:

javac -cp .:rhino.jar SheetJSRhino.java
jar -cf SheetJS.jar SheetJSRhino.class com/sheetjs/*.class

4) Download https://sheetjs.com/pres.xlsx and test:

java -cp .:SheetJS.jar:rhino.jar SheetJSRhino pres.xlsx

Legacy Engines

danger

These examples were written when the engines were maintained. New projects should not use these engines. The demos are included for legacy deployments.

ChakraCore

caution

ChakraCore was an open source JavaScript engine released by Microsoft. It was a fork of the Chakra engine that powered Internet Explorer. When Microsoft Edge switched to become a fork of Chromium, Microsoft stopped providing support.

ChakraCore is an embeddable JS engine written in C++. The library and binary distributions include a command-line tool chakra for running JS scripts.

The simplest way to interact with the engine is to pass Base64 strings. The make target builds a very simple payload with the data.

note

The official release includes the ch standalone binary. While applications should link against the official libraries, the standalone tool is useful for verifying functionality.

Complete Example (click to show)

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) Download and extract the ChakraCore release ZIP. Copy the binary (bin/ch) to your project folder.

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

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

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

3) Create support scripts:

  • global.js creates a global variable:
global.js
var global = (function(){ return this; }).call(null);
  • chakra.js will call XLSX.read and XLSX.utils.sheet_to_csv:
chakra.js
/* sheetjs (C) 2013-present  SheetJS -- http://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.chakra.js:

cat global.js xlsx.full.min.js payload.js chakra.js > xlsx.chakra.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 ChakraCore standalone binary:

./ch xlsx.chakra.js

Nashorn

caution

Nashorn shipped with Java 8. It was deprecated in Java 11 and was officially removed in JDK 15. New Java applications should use Rhino.

Nashorn ships with Java. It includes a command-line tool jjs for running JS scripts. It is somewhat limited but does offer access to the full Java runtime.

The load function in jjs can load the minified source directly:

var global = (function(){ return this; }).call(null);
load('xlsx.full.min.js');

The Java nio API provides the Files.readAllBytes method to read a file into a byte array. To use in XLSX.read, the demo copies the bytes into a plain JS array and calls XLSX.read with type "array".

Complete Example (click to show)

0) Ensure jjs is available on system path

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

2) Save the following script to SheetJSNashorn.js:

SheetJSNashorn.js
/* sheetjs (C) 2013-present  SheetJS -- http://sheetjs.com */

/* load module */
var global = (function(){ return this; }).call(null);
load('xlsx.full.min.js');

/* helper to convert byte array to plain JS array */
function b2a(b) {
var out = new Array(b.length);
for(var i = 0; i < out.length; i++) out[i] = (b[i] < 0 ? b[i] + 256 : b[i]);
return out;
}

function process_file(path) {
java.lang.System.out.println(path);

/* read file */
var path = java.nio.file.Paths.get(path);
var bytes = java.nio.file.Files.readAllBytes(path);
var u8a = b2a(bytes);

/* read data */
var wb = XLSX.read(u8a, {type:"array"});

/* get first worksheet as an array of arrays */
var ws = wb.Sheets[wb.SheetNames[0]];
var js = XLSX.utils.sheet_to_json(ws, {header:1});

/* print out every line */
js.forEach(function(l) { java.lang.System.out.println(JSON.stringify(l)); });
}

process_file('pres.numbers');

3) Test the script:

jjs SheetJSNashorn.js

It will print out the first worksheet contents.