VB.NET

Call a JavaScript Function Returning an Integer

See more JavaScript Examples

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)

JavaScript

function calculateScore(name, pointsA, pointsB) {
    // Return length of name + both scores
    return name.length + pointsA + pointsB;
    }