Pas2js : What is it ?
- as a library
- as a command-line program
- as a webserver
It transpiles from actual pascal source, it has no intermediate .ppu file. That means all sources must always be available.
through import units (comparable to the windows or unix units for the native compiler).
- For nodejs, basic support for the nodejs runtime environment is available.
- An import unit for jQuery is available (libjquery)
pas2js can automatically include this file in the generated output, like this:
pas2js -Jc -Jirtl.js -Tbrowser hello.pas
There is a basic Object Pascal RTL, several units from the FPC Packages are also available
- DB (yes, TDataset)
- fpcunit testsuite
- web (browser provided objects)
- libjquery (jquery is available too)
- nodejs (basic node runtime environment)
- browserconsole (support writeln)
Where to get it
The pas2js compiler is - naturally - open source and can be downloaded and used freely. The sources are currently the primary means to get it.
- The Pas2js compiler is part of Free Pascal. As such, the compiler is present in the utils/pas2js directory of the
- The pas2js RTL is still in flux. To enable faster releases, the RTL and demos are in a separate repository in SVN:
svn co https://svn.freepascal.org/svn/projects/pas2js/trunk pas2js
Till pas2js is integrated in the main FPC distribution, snapshots will be made available as time permits. They will contain binaries for Windows, Linux (64 bit) and Macos.
A beta snapshot can be found for the following versions:
How to use pas2js
The command-line arguments are kept mostly the same as the FPC command-line arguments. Error messages are also in the same format.
The compiler needs access to all sources, and so you need to specify the path to the sources of all used units.
As for the FPC compiler, a configuration file is supported, which has the same syntax as the FPC config file.
Basically, the command is the same as any FPC command line. The only thing that is different is the target: browser or nodeejs
Here is the complete list of command line arguments.
for the browser
Consider the classical:
program hello; begin Writeln('Hello, world!'); end.
Yes, writeln is supported. Here is how to compile it:
pas2js -Jc -jirtl.js -Tbrowser hello.pas
When compiled succesfully, the code can be run in the browser by opening a html file in the browser with the following content:
The files that are needed are:
Whether hello.html is opened by double-clicking it in the explorer or put on a server and opened with an URL, is not relevant for the functioning.
The output is visible in the browser's web developer console. By including the browserconsole unit, it will be visible in the browser page:
program hello; uses browserconsole; begin Writeln('Hello, world!'); end.
pas2js -Tnodejs hello.pas
When compiled succesfully, the code can be run in node using the following command.
Supported syntax elements
Basically, Delphi 7 syntax minus interfaces is supported. This includes RTTI. A more detailed list can be found in the translation.html file in the sources.
There are some constructs that are naturally not supported and will never be supported: Anything involving memory pointers.
Planned language features
Basically, the idea is to get the pas2js transpiler up to the same level as FPC or Delphi. That means the following needs to be added:
- More runtime/compile time checks
- Type helpers
- Anonymous functions
Needless to say, anything requiring direct memory access is not going to be supported.
Lazarus integration of pas2js
Lazarus understands the concept of external classes as used by pas2js, so code completion will work.
pas2js comes with several lazarus packages that 'import' the pas2js rtl units: by doing so, the IDE will know which units to use.
- pas2js_rtl : the basic RTL
- fcl_base_pas2js: The custapp and other units
- fpcunit_pas2js: the fpcunit units
- pas2js_fcldb: the database units
A new project wizard is under construction, but deeper integration with lazarus is planned.
Moreover, the transpiler can generate a source map, which means that you will be able to see and debug the pascal code in the browser. (not everything will work, but many things do)