docs.sheetjs.com/docz/docs/03-demos/42-engines/04-jsc.md

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import current from '/version.js'; import CodeBlock from '@theme/CodeBlock';

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.

The SheetJS Standalone scripts can be parsed and evaluated in a JSC context.

:::warning Platform Limitations

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

:::

Integration Details

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

Initialize JavaScriptCore

JSC does not provide a global variable. It can be created in one line:

var context: JSContext!
do {
  context = JSContext();
  context.exceptionHandler = { _, X in if let e = X { print(e.toString()!); }; };
  // highlight-next-line
  context.evaluateScript("var global = (function(){ return this; }).call(null);");
} catch { print(error.localizedDescription); }

Load SheetJS Scripts

The main library can be loaded by reading the scripts from the file system and evaluating in the JSC context:

let src = try String(contentsOfFile: "xlsx.full.min.js");
context.evaluateScript(src);

To confirm the library is loaded, XLSX.version can be inspected:

let XLSX: JSValue! = context.objectForKeyedSubscript("XLSX");
if let ver = XLSX.objectForKeyedSubscript("version") { print(ver.toString()); }

Reading Files

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'});");

Direct Read (click to show)

Uint8Array data can be passed directly, skipping string encoding and decoding:

let url = URL(fileURLWithPath: file)
var data: Data! = try Data(contentsOf: url);
let count = data.count;
/* Note: the operations must be performed in the closure! */
let wb: JSValue! = data.withUnsafeMutableBytes { (dataPtr: UnsafeMutableRawBufferPointer) in
// highlight-next-line
  let ab: JSValue! = JSValue(jsValueRef: JSObjectMakeTypedArrayWithBytesNoCopy(context.jsGlobalContextRef, kJSTypedArrayTypeUint8Array, dataPtr.baseAddress, count, nil, nil, nil), in: context)
  /* prepare options argument */
  context.evaluateScript(String(format: "var readopts = {type:'array', dense:true}"));
  let readopts: JSValue = context.objectForKeyedSubscript("readopts");
  /* call XLSX.read */
  let XLSX: JSValue! = context.objectForKeyedSubscript("XLSX");
  let readfunc: JSValue = XLSX.objectForKeyedSubscript("read");
  return readfunc.call(withArguments: [ab, readopts]);
}

For broad compatibility with Swift versions, the demo uses the String method.

Writing Files

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);

Complete Example

:::note

This demo was tested in the following environments:

Architecture	Swift	Date
darwin-x64	5.8.1	2023-07-24
darwin-arm	5.8.1	2023-06-05

:::

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

:::caution This demo only runs on MacOS

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

:::

0. Ensure Xcode is installed. Create a folder for the project:

mkdir sheetjswift
cd sheetjswift

1. Download the SheetJS Standalone script and the test file. Save both files in the project directory:

• xlsx.full.min.js
• pres.numbers

{\ curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js curl -LO https://sheetjs.com/pres.numbers}

2. Download the Swift scripts for the demo

• SheetJSCore.swift Wrapper library
• main.swift Command-line script

curl -LO https://docs.sheetjs.com/swift/SheetJSCore.swift
curl -LO https://docs.sheetjs.com/swift/main.swift

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.