Pascal (Lazarus/Delphi)

Call a JavaScript Function Returning an Integer

See more JavaScript Examples

Demonstrates how to call a JavaScript function that returns an integer. Pascal (Lazarus/Delphi)

program ChilkatDemo;

// Demonstrates using the Chilkat Pascal wrapper via the C bridge DLL.
// Builds as a console application under Lazarus (FPC) or Delphi.

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
{$APPTYPE CONSOLE}

uses
  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}
  SysUtils,
  CkDllLoader,
  Chilkat.Js,
  Chilkat.StringBuilder,
  Chilkat.JsonObject;

// ---------------------------------------------------------------------------

procedure RunDemo;
var
  success: Boolean;
  sbScript: TStringBuilder;
  js: TJs;
  result: TJsonObject;
  funcCall: TJsonObject;
  retval: Integer;

begin
  success := False;

  //  ----------------------------------------------------------------------------------
  //  The Javascript function called in this example is shown at the bottom of this page.
  //  -----------------------------------------------------------------------------------

  //  In this example, we'll load the Javascript function definition from a file.
  //  It doesn't need to come from a file.  It could just as easily be loaded from a string.
  sbScript := TStringBuilder.Create;
  success := sbScript.LoadFile('js_call_function.js','utf-8');
  if (success = False) then
    begin
      WriteLn(sbScript.LastErrorText);
      Exit;
    end;

  //  Note: Each instance of a Chilkat Js object automatically establishes
  //  its own internal runtime and context.  Applications do not need to explicitly create
  //  the JavaScript runtime or context.
  js := TJs.Create;

  result := TJsonObject.Create;
  result.EmitCompact := False;

  //  Call Eval to add the function (shown at the bottom of this page) to the context's global object
  success := js.Eval(sbScript,result);
  if (success = False) then
    begin
      //  Examine the result for an exception.
      WriteLn(result.Emit());

      //  Also examine the LastErrorText.
      WriteLn(js.LastErrorText);
      Exit;
    end;

  WriteLn(result.Emit());

  //  The expected output is "undefined":

  //  {
  //    "type": "undefined",
  //    "value": "undefined"
  //  }

  //     When Eval processes a script containing only a function declaration,
  //     it successfully performs the action (the function becomes defined).
  //     However, since the script consists of a statement that produces no value,
  //     the script's overall completion value is empty. In JavaScript, the
  //     absence of a value is represented by `undefined`.
  //  
  //     Therefore, the Eval call returns `undefined`.

  //  ------------------------------------------------------------------------------
  //  Call the function calculateScore("Player1", 10, 20)

  funcCall := TJsonObject.Create;

  //  Create JSON defining the function call:

  //  {
  //    "name": "calculateScore",
  //    "args": [ "Player1", 10, 20 ]
  //  }

  funcCall.UpdateString('name','calculateScore');
  funcCall.UpdateString('args[0]','Player1');
  funcCall.UpdateInt('args[1]',10);
  funcCall.UpdateInt('args[2]',20);

  funcCall.EmitCompact := False;
  WriteLn(funcCall.Emit());

  success := js.CallFunction(funcCall,result);
  if (success = False) then
    begin
      //  Examine the result for an exception.
      WriteLn(result.Emit());

      //  Also examine the LastErrorText.
      WriteLn(js.LastErrorText);
      Exit;
    end;

  WriteLn(result.Emit());

  //  Output:

  //  {
  //    "type": "int",
  //    "value": 37
  //  }

  retval := result.IntOf('value');
  WriteLn('retval = ' + retval);


  sbScript.Free;
  js.Free;
  result.Free;
  funcCall.Free;

end;

// ---------------------------------------------------------------------------

begin

  try
    RunDemo;
  except
    on E: Exception do
      WriteLn('Unhandled exception: ', E.ClassName, ': ', E.Message);
  end;

  WriteLn;
  {$IFDEF MSWINDOWS}
  WriteLn('Press Enter to exit...');
  ReadLn;
  {$ENDIF}
end.