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Other JS Engines and Deployments

There are many JS engines and deployments outside of web browsers. NodeJS is the most popular deployment, but there are many others for special use cases. Some optimize for low overhead and others optimize for ease of embedding within other applications. Since it was designed for ES3 engines, the library can be used in those settings! This demo tries to demonstrate a few alternative deployments.

Some engines provide no default global object. To create a global reference:

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

Swift + JavaScriptCore

iOS and OSX ship with the JavaScriptCore framework, enabling easy JS access from Swift and Objective-C. Hybrid function invocation is tricky, but explicit data passing is straightforward. The demo shows a standalone example for OSX. For playgrounds, the library should be copied to shared playground data directory (usually ~/Documents/Shared Playground Data):

/* This only works in a playground, see SheetJSCore.swift for standalone use */
import JavaScriptCore;
import PlaygroundSupport;

/* build path variable for the library */
let shared_dir = PlaygroundSupport.playgroundSharedDataDirectory;
let lib_path = shared_dir.appendingPathComponent("xlsx.full.min.js");

/* prepare JS context */
var context: JSContext! = JSContext();
var src = "var global = (function(){ return this; }).call(null);";
context.evaluateScript(src);

/* load library */
var lib = try? String(contentsOf: lib_path);
context.evaluateScript(lib);
let XLSX: JSValue! = context.objectForKeyedSubscript("XLSX");

/* to verify the library was loaded, get the version string */
let XLSXversion: JSValue! = XLSX.objectForKeyedSubscript("version")
var version  = XLSXversion.toString();

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

/* parse sheetjs.xls */
let file_path = shared_dir.appendingPathComponent("sheetjs.xls");
let data: String! = try String(contentsOf: file_path, encoding: String.Encoding.isoLatin1);
context.setObject(data, forKeyedSubscript: "payload" as (NSCopying & NSObjectProtocol)!);
src = "var wb = XLSX.read(payload, {type:'binary'});";
context.evaluateScript(src);

/* write to sheetjsw.xlsx  */
let out_path = shared_dir.appendingPathComponent("sheetjsw.xlsx");
src = "var out = XLSX.write(wb, {type:'binary', bookType:'xlsx'})";
context.evaluateScript(src);
let outvalue: JSValue! = context.objectForKeyedSubscript("out");
var out: String! = outvalue.toString();
try? out.write(to: out_path, atomically: false, encoding: String.Encoding.isoLatin1);

Nashorn

Nashorn ships with Java 8. 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".

Rhino

Rhino is an ES3+ engine written 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);

ChakraCore

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.

Duktape

Duktape is an embeddable JS engine written in C. The amalgamation makes integration extremely simple! It supports Buffer natively:

/* 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, {type:'buffer'});");

/* 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);

Goja

Goja is a pure Go implementation of ECMAScript 5. As of this writing, there are some issues with processing Unicode data, but the xlsx.core.min.js script can be processed. []byte should be transformed to a binary string in the engine:

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

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

/* convert to binary string */
_, _ = vm.RunString("var bstr = ''; for(var i = 0; i < buf.length; ++i) bstr += String.fromCharCode(buf[i]);")

/* parse */
wb, _ = vm.RunString("wb = XLSX.read(bstr, {type:'binary', cellNF:true});")

On the write side, "base64" strings can be decoded in Go:

b64str, _ := vm.RunString("XLSX.write(wb, {type:'base64', bookType:'xlsx'})")
buf, _ := base64.StdEncoding.DecodeString(b64str.String())
_ = ioutil.WriteFile("sheetjs.xlsx", buf, 0644)

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