B4X: Writing JavaScript with ABMaterials B4JS

B4JS

After a delay of more of a year working on other ABM stuff, I finally got back on track with B4JS. I will make a series of tutorials explaining how it works. B4JS is part of the ABMaterial library 4.25 which is going to be released next week.

INTRODUCTION

One way to look at B4JS is as some kind of new platform in B4X, that uses a very similar syntax as B4J. At runtime, the B4J source code is transpiled to pure JavaScript. The generated source code can then be used in e.g. an ABMaterial Web App, or maybe even as a base for another JavaScript library.

A typical B4JS class could look like this:

Sub Process_Globals
   Dim myString As String
   Public pubMap As Map

   Dim timer As Timer
   Dim myGlobalName As String = "GlobalAlain"
End Sub
'Initializes the object. You can NOT add parameters.
Public Sub InitializeB4JS()
   pubMap.Initialize

   Dim myName As String = "Alain"
   ' smartstrings do not support date, time or xml functions
   myString = $"Hello planet "B4X"! This is a test
    from ${myName} and ${myGlobalName}"$
   Log("myString.Contains('planet'): " & myString.Contains("planet"))
   Dim myLocalInt As Int = 15
   myLocalInt = myLocalInt * myString.Length

   LogMe("15 x the length of " & myString & " = " & myLocalInt)

   For i=0 To 50
       myLocalInt = myLocalInt + 2
       Select Case myLocalInt
           Case 20, 40
               Log(i)
               pubMap.Put("key" & i, i)
           Case Else
               Log("less than 20")
       End Select
   Next

   timer.Initialize("timer", 1000)
   timer.Enabled = True

   Dim sb As StringBuilder
   sb.Initialize
   sb.Append("lijn 1").Append(CRLF).Append("lijn 2")
   Log(sb.ToString)
   Log(sb.Length)
   sb.Insert(2,"X")
   Log(sb.ToString)
   sb.Remove(2,3)
   Log(sb.ToString)
End Sub
Private Sub Timer_Tick
   timer.Enabled = False
   Log("timer ticking")
   If timer.Enabled = False Then
       timer.Interval = timer.Interval + 1000
       Log("timer new interval: " & timer.Interval)
       timer.Enabled = True
   End If
End Sub

Looks very familiar, no? :)

Having the browser doing some stuff using JavaScript can have some big advantages by relieving some pressure from your server (checking if a form is filled in correctly, or changing the visibility of an ABMContainer if a user clicks a button).

But it also demands a great responsibility from the programmer not to expose to much information to the user. Never, ever write sensitive stuff like SQL, passwords etc in B4JS!

Another advantage is being able to expose some events (like the KeyUp/KeyDown events in an ABMInput field). They are deliberately omitted in ABM, because such events could potentially kill your server. But in Javascript, we could use them e.g. to check if the user could entry numbers, or if fits an email mask.

Having a Timer running on the browser side can also be handy.

First an overview of the syntax B4JS can handle:

OVERVIEW

Core library
Variable types:

Bit:

String:

List:

Map:

StringBuilder:

DateTime:

Keywords:

Operators:

Control Structures:

Timer:

Smart String Literal:

JSON library
JSONParser:

JSONGenerator:

ABMaterial library (as of 2018/03/10, for the latest list check the B4X forum):
ABMLabel:

EVENTS: B4JSOnClick, B4JSOnMouseEnter, B4JSOnMouseLeave

ABMInput:

ABMContainer:

ABMSwitch:

ABMCheckbox:

ABMRadioGroup:

ABMButton:

ABMPage:

ABMRow:

B4JSUniqueKey

EVENTS: B4JSOnClick, B4JSOnMouseEnter, B4JSOnMouseLeave

ABMCell:

B4JSUniqueKey

EVENTS: B4JSOnClick, B4JSOnMouseEnter, B4JSOnMouseLeave

TUTORIALS

In the next following days, I would like to cover the following topics:

01. Getting started
02. Core functions
03. Inline JavaScript
04. Running JavaScript on the server side (mini NodeJS?)
05. JSON & Ajax Calls
06. The UI (ABMaterial) connection

Alwaysbusy

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