![● Simple to fix: ST blocks always answer some value
○ ST result := [123]
○ JS result = () =>{return 123}
● Complex to fix: ST blocks support non-local returns
○ ST condition ifTrue: [^123]
○ JS rely on exceptions
19
Example: Block Returns](https://image.slidesharecdn.com/iwst-101-bour-dynamic-lang-transpilation-250724075418-6fd3c010/85/Challenges-of-Transpiling-Smalltalk-to-JavaScript-19-320.jpg)
Challenges of Transpiling Smalltalk to JavaScript
- 1. Challenges of Transpiling Smalltalk to JavaScript Noury Bouraqadi & Dave Mason International Workshop on Smalltalk Technologies Gdansk, Poland; July 1st to 4th, 2025
- 2. Why Transpile Smalltalk to JavaScript? 2
- 3. Why Transpile Smalltalk to JavaScript? ST Simple & clean semantics Rich IDE & core libraries 3 JS Ubiquitous deployment Performance Large ecosystem
- 4. Why Transpile Smalltalk to JavaScript? ST Simple & clean semantics Rich IDE & core libraries 4 Wednesday July 2nd 2025 JS Ubiquitous deployment Performance Large ecosystem ● ST + JS = Best of both worlds ● Smalltalk community interest in the Web/JavaScript ○ ESUG Main Track Talk Smalltalk for the Web
- 5. 5 Transpilation = TRANSlation & comPILATION Transpiler 100% Smalltalk Program 100% JavaScript Program
- 6. 6 Transpilation = TRANSlation & comPILATION Transpiler 100% Smalltalk Program 100% JavaScript Program Valid Valid
- 7. 7 Transpilation = TRANSlation & comPILATION Transpiler 100% Smalltalk Program 100% JavaScript Program Semantically Equivalent Valid Valid
- 9. 9 How to Transpile Smalltalk to JavaScript?
- 10. ○ Map Smalltalk’s syntax to JavaScript? ○ Map Smalltalk’s reflective kernel to JavaScript? ○ Handle Smalltalk dependencies with the runtime? 10 How to Transpile Smalltalk to JavaScript?
- 11. ○ Map Smalltalk’s syntax to JavaScript? ○ Map Smalltalk’s reflective kernel to JavaScript? ○ Handle Smalltalk dependencies with the runtime? 11 How to Transpile Smalltalk to JavaScript? Empirical Study based on 10 Year experience with
- 12. ○ Map Smalltalk’s syntax to JavaScript? ○ Map Smalltalk’s reflective kernel to JavaScript? ○ Handle Smalltalk dependencies with the runtime? 12 How to Transpile Smalltalk to JavaScript? Challenges Catalog 1. Primitive Types & Literals 2. Messages 3. Block Closures 4. Classes 5. Reflection Empirical Study based on 10 Year experience with
- 14. ● JS 𝑢𝑛𝑑𝑒𝑓𝑖𝑛𝑒𝑑 and 𝑛𝑢𝑙𝑙 are Not Objects. ● JS has an Impoverished Numeric Stack. ● ST Automatically Converts ○ Between Small Integers & Large Ones. ● ST Supports Fixed-Point Arithmetic. ● ST has Literal Symbols. 14 Challenges: Primitive Types and Literals
- 15. ● JS has a 𝑆𝑦𝑚𝑏𝑜𝑙 class, but: ○ No literal symbols ■ Simple to fix ● Map ST symbols to instances of JS Symbol ○ JS Symbol class is not related to String! ■ Complex to fix ● Make Symbol subclass of String ○ Side-effects? ● Override some String methods 15 Example: ST Literal Symbols
- 16. ● Non-Alphanumeric Characters in ST Message Selectors ● JS Math-Like Message Priorities ● ST Message Cascading 16 Challenges: Messages
- 17. ● Simple to fix: ○ Replace non-alphanumeric characters with their Ascii code ○ ST keyword selectors: 1 string concatenating keywords ● Complex to fix: None 17 Example: Non-Alphanumeric Characters in Selectors
- 18. Smalltalk Blocks: ● Always Bind the Outer Context ● Always Answer Some Value ● Support Non-Local Returns 18 Challenges: Block Closures
- 19. ● Simple to fix: ST blocks always answer some value ○ ST result := [123] ○ JS result = () =>{return 123} ● Complex to fix: ST blocks support non-local returns ○ ST condition ifTrue: [^123] ○ JS rely on exceptions 19 Example: Block Returns
- 20. ● Class Variables ● Pool Variables ● Class Extensions ● Stateful Traits 20 Challenges: ST Classes - 1
- 21. ● Class Initialization & Startup/Shutdown Lists ● Methods Always Have a Return Value ● Methods can Have Pragmas ○ Primitive Pragmas Refer to the Virtual Machine 21 Challenges: ST Classes - 2
- 22. ● Simple to fix: Class Variables ○ JS Classes are objects with attributes ○ JS encapsulation is optional class A{ anInstanceMethod(){ x = A.someClassVariable + 42; } } A.someClassVariable = 37; 22 Examples - 1
- 23. ● Complex to fix: Pragmas such as #primitive: ○ Implement the primitive behavior 23 Examples - 2
- 24. ● ST Reifies Messages Upon Handling Type Errors ● ST Reifies Execution Contexts ● ST and JS have different solutions for Intercepting Method Evaluation ● Pharo ST Reifies Slots ● Pharo ST classes define Object Format/Layout 24 Challenges: Reflection
- 25. ● Simple to fix: ST DNU Reifies Messages ○ Extend JS Object with ■ doesNotUnderstand() method ■ default methods for every sent message in ST Code Object.prototype.zork = function(arg1, arg2){ return this.doesNotUnderstand(“zork”, arguments)} 25 Examples - 1
- 26. ● Complex to fix: ST Reifies Execution Contexts ○ ST thisContext 26 Examples
- 27. Smalltalk & JavaScript 100% semantic equivalence via transpilation is difficult if not impossible! 27 Conclusion
- 28. ● Some challenges are “easy” to address ○ Primitive Types & Literals, ○ Messages, ○ Block Closures ● Several ST capabilities are complex to implement in JS ○ Primitives, ○ thisContext, ○ Reified Slots… 28 Conclusion: Not all challenges are equal
- 29. ● Beyond Transpilation ○ ST and JS Run-time interoperability (Production) ○ Live-coding with JS objects from the ST (Development) ○ Reuse JS libraries (code + globals) in code transcribed from ST ○ Transpile ST to produce JS libraries for 3rd parties. ● Methodology? ○ Generalizable to other language pairs? Smalltalk & Python? 29 Future Work
- 30. Develop in Pharo, Run on JavaScript PharoJS.org Kindly Supported by Thanks to all the contributors! M IT License
- 31. Challenges of Transpiling Smalltalk to JavaScript Noury Bouraqadi & Dave Mason International Workshop on Smalltalk Technologies Gdansk, Poland; July 1st to 4th, 2025