VB.NET

Call a JavaScript Function Returning an Integer

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Demonstrates how to call a JavaScript function that returns an integer. VB.NET

Dim success As Boolean = 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.
Dim sbScript As New Chilkat.StringBuilder
success = sbScript.LoadFile("js_call_function.js","utf-8")
If (success = False) Then
    Debug.WriteLine(sbScript.LastErrorText)
    Exit Sub
End If


' 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.
Dim js As New Chilkat.Js

Dim result As New Chilkat.JsonObject
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
    ' 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 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)

Dim funcCall As New Chilkat.JsonObject

' 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
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())

' Output:

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

Dim retval As Integer = result.IntOf("value")
Debug.WriteLine("retval = " & retval)