VB.NET

Call a JavaScript Function Passing an Object Argument

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Demonstrates how to call a JavaScript function with an argument that is an object. VB.NET

Dim success As Boolean = False

' This is the JavaScript function we'll call:

' function describeCar(car) {
' 	console.log(`This is a ${car.year} ${car.make} ${car.model}.`);
' }

Dim sbScript As New Chilkat.StringBuilder
sbScript.Append("function describeCar(car) { console.log(`This is a ${car.year} ${car.make} ${car.model}.`); }")

Dim js As New Chilkat.Js

Dim result As New Chilkat.JsonObject
result.EmitCompact = False

' Call Eval to add the function to the context's global object
success = js.Eval(sbScript,result)
If (success = False) Then
    ' Examine the result for an exception.
    Debug.WriteLine(result.Emit())

    ' Also examine the LastErrorText.
    Debug.WriteLine(js.LastErrorText)
    Exit Sub
End If


' ------------------------------------------------------------------------------
' Call the function describeCar(car)

Dim funcCall As New Chilkat.JsonObject
funcCall.EmitCompact = False

' Create JSON specifying the function name and arguments
' In this case, there is only 1 argument, and it is an object.

' {
'   "name": "describeCar",
'   "args": [
'     {
'       "make": "Toyota",
'       "model": "Corolla",
'       "year": 2022
'     }
'   ]
' }

funcCall.UpdateString("name","describeCar")

' Create the JSON object that is the argument.
Dim arg As New Chilkat.JsonObject
arg.UpdateString("make","Toyota")
arg.UpdateString("model","Corolla")
arg.UpdateInt("year",2022)

' Create the arguments array.
Dim argsArray As New Chilkat.JsonArray
argsArray.AddObjectCopyAt(0,arg)

' Add the "args" array to the funcCall.
funcCall.AppendArrayCopy("args",argsArray)

Debug.WriteLine(funcCall.Emit())

success = js.CallFunction(funcCall,result)
If (success = False) Then
    ' Examine the result for an exception.
    Debug.WriteLine(result.Emit())

    ' Also examine the LastErrorText.
    Debug.WriteLine(js.LastErrorText)
    Exit Sub
End If


Debug.WriteLine(result.Emit())

' The describeCar JavaScript function returns nothing. 
' Therefore, the result is "undefined".

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

' However, the function emitted text to the console.

Dim sbOut As New Chilkat.StringBuilder
js.ConsoleOutputSb(sbOut)
Debug.WriteLine(sbOut.GetAsString())

' Output:
' This is a 2022 Toyota Corolla.

' -----------------------------------------------------------
' Note: If the object argument is simple, this is an alternative
' and simpler way of creating the funcCall:

funcCall.Clear()
funcCall.UpdateString("name","describeCar")
funcCall.UpdateString("args[0].make","Toyota")
funcCall.UpdateString("args[0].model","Corolla")
funcCall.UpdateInt("args[0].year",2022)
Debug.WriteLine(funcCall.Emit())