Substrata-Swift

Small, Efficient, Easy. Javascript Engine for Swift.

Using JavascriptCore (and other engines in the future) has been simplified. No more messing with JSValues, type conversion and messy call sites to use Javascript.

Substrata Swift is currently only available in Beta

Quick Start

Values are converted automatically to the appropriate types as needed. Calls into JavascriptCore are all synchronized on the same serial dispatch queue.

// get a shared engine instance
let engine = JSEngine.shared

// set the error handler we want to use
engine.errorHandler = { error in
   print("javascript error: \(error)")
}

// execute some js
let result = engine.execute(script: "1 + 2;") as? Int
if result == 3 {
   // success!
}

Loading a Javascript bundle from disk

Load a bundle from disk. Only accepts file URLs. Any downloading of javascript bundles must be done upstream by the caller. A completion block will be executed when done (if specified).

engine.loadBundle(url: myBundleURL) { error in
   if error {
       print("oh noes, we failed: \(error))
       return
   } else {
       success = true
   }
}

Expose and Extend

Expose a native class to Javascript by name.

Classes that will be exposed need to have a protocol marked with JSExports to allow any methods or properties to be accessible.

If you intend on allowing the class to be used as a return value or parameters it may also be useful to conform to JSConvertible.

protocol MyClassExports: JSExport {
   var myValue: Int
   func doSomething() -> Bool
}

@objc
class MyClass: NSObject, MyClassExports, JSConvertible {
   var myValue: Int = 5
   func doSomething() -> Bool { return true }
}

engine.expose(classType: MyClass.type, name: "MyClass")

let something = engine.execute(script: "var c = new MyClass(); c.doSomething();") as? Bool
if something {
   // success!
}

let jsClassInstance = engine.execute(script: "c;") as? MyClass
if jsClassInstance {
   jsClassInstance.doSomething()
}

Expose a native function to Javascript by name.

let quadruple: @convention(block) (Int) -> Int = { input in
    return input * 4
}

engine.expose(function: quadruple, name: "quadruple")
let result = engine.execute(script: "quadruple(3);") as? Int
if result == 12 {
   // success!
}

Extend an existing Javascript object.

let doSomething: @convention(block) () -> Void = {
    print("hello")
}

engine.extend(object: "console", function: doSomething, name: "doSomething")

Access and Use Javascript

Call a Javascript function directly by name. Javascript handles the name resolution.

let result = engine.call(functionName: "thing.addNumbers", params: [1, 2, 3]) as? Int
if result == 6 {
   // success!
}

Just run some Javascript code freely...

let something = engine.execute(script: "var c = new MyClass(); c.doSomething();") as? Bool
if something {
	// success!
}

Grab and Set some value on the global object.

engine.setObject(key: "numberArray", value: [1, 2, 3])
let numnums = engine.object(key: "numberArray") as? [Int]

Why not use JavascriptCore directly?

Cuz it's kind of a pain. Much of JavascriptCore puts the onus to make any niceties, like type conversion, logic checks, etc. on the caller and tends to lead to some code that looks like spaghetti.

We also wanted to set ourselves up a little for a world where JavascriptCore isn't the only option without rewriting the calling code.

License

MIT License

Copyright (c) 2022 Segment

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.