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Pascal to Javascript Compiler

For creating the single-page JavaScript application, the Pascal code of your project is compiled to JavaScript and this JavaScript application runs in the browser. Typically a connection to the server will be made by HTTP REST requests or via WebSocket communication. To compile the Pascal code to JavaScript code, the pas2js compiler is used that is an open-source project and builds on years of experience of the FPC compiler team. More information about the pas2js project can be found here:

At this moment, this support for the Pascal language is highly compatible with the Delphi language. Some newer Delphi language features are not yet supported in v1.0 though but are on the roadmap. The language features not yet supported but planned for the 2018 – 2019 timeframe are:

  • Generics
  • Attributes
  • Advanced Records
  • Advanced RTTI
  • Type helpers
  • Anonymous functions

For more details about the capabilities of the pas2js compiler, please refer to

TMS WEB Core ships with a validated version of the pas2js compiler. We recommend using the pas2js compiler included in the TMS WEB Core distribution as this is the version we test & approve our entire framework and IDE integration with.


Equally important to move existing VCL or FMX code bases to the web is the support for RTL. A huge part of the Delphi RTL is available and delivered with the compiler. This includes now:

There is a basic Object Pascal RTL, several units from the FPC Packages are also available

  • system
  • sysutils
  • math
  • strutils
  • rtlconst
  • classes
  • contnrs
  • typinfo
  • objpas
  • dateutils
  • DB
  • js (javascript system objects)
  • web (browser provided objects)
  • libjquery

For more information about RTL support, please see:


As a webbrowser does not know the concept of DFM files to load form configuration from and as the form designer in the Delphi IDE is technically a VCL form, there is before compiling the code to JavaScript a preprocessing step. This preprocessing step handles the conversion from DFM file to code for initialization of the form. The pre-processor will also convert the unit namespaces from VCL to WEBLib. This unit namespace conversion not only applies to unit names but also when unit name prefixes are explicitly used for types. If there is a special reason to disallow the pre-processor to skip lines in the code, prefix these lines with the {NOPP} specifier.

So, the line

will be converted to
The line
{NOPP} VCL.MyUnit.MyType
will remain as-is before it is being compiled, i.e.