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van_dml.js: Auto-Append feature to VanJS

Author: Eckehard

van_dml.js adds a new flavour of composition to VanJS. This is heavily inspired by the DML-framework for dynamic page creation.

Van_DML extends the core of VanJS. You can enable van_dml like this:

<script src="https://cdn.jsdelivr.net/gh/vanjs-org/van/public/van-latest.nomodule.min.js"></script>
<script src="https://cdn.jsdelivr.net/gh/vanjs-org/van/addons/van_dml/src/van_dml.js"></script>

<script>
    const { h1, h2, div, p, button } = van.tags;
    const { begin, end, base, sp, css } = van  // new functions of van_dml
</script>

How does it work?

begin(ID) selects an element "ID" as a base. ID can be a DOM element or a HTML-ID. All elements created after begin() are automatically appended as children to this object. end() finishes the automatic appending.

begin() and end() can be nested like this:

    const { h1, h2, div, p, button } = van.tags;
    const { begin, end, base, sp, css } = van

    begin(document.body)
        h1("Headline")
        begin(div({style: "border: 1px solid black"}))
            h2("Headline in a box")
            p("some text here")
        end()
    end()

This is similar to using plain HTML, where a tag create elements directly.

transparent operation of "begin()"

Van-Tags return a DOM Reference that can be stored in a variable:

    let d = div()
    d.style.color = "red"
    d.appendChild(h1("Headline");

With VAN_DML, this can be rewritten:

    let d = begin(div()) // -> d is the <div>-element
    begin(div()).style.color = "red" // Access the style of div

begin() is "transparent", it just returns the DOM reference of the first child. This let´s you create functions like this:

    const bdiv = (...args) => begin(div(...args))
    
    bdiv() // Create a div and open for append
        h1()
    end()

begin(ID) can also digest Strings:

    <div id="ID"></div>
    <script>
    begin("ID") // select div by ID
        h1()
    end()
    </script>

end(n)

end() finishes the append mode and returns to the previous base. For each begin() there should be one call of end(). You can verify this by checking SP() === 0 (see below). If no base is selected (or the calls begin() and end() are balanced), auto-Append is disabled.

end(n) runs end() n times. May be convenient to return from deep nested functions.

base() and sp()

base() returns the current base:

    begin(div()) 
    let b = base(); // returns the current base (div())

sp() is the current Stack-Position. Initially sp() is 0. With each call of begin() sp() is incremented, end() decrements sp(). To check your code, you can add this line to the end of Javascript:

    begin(document.body) 
       .... some code here
    end()
    
    if (sp() !== 0) alert(`baseStack mismatch: stacksize ${sp()} at end of Javascript`)

css(): create CSS-rules dynamically with Javascript

css(s) adds new CSS-rules during runtime.
s can be

  • a string css(".myClass { color: red; }")
  • a template string with multiple rules
    css(`
        .myClass { color: red; }
        .myClass: hover { color: green }
    `)
  • It can contain template literals:
   let color = [ "red", "green", "blue" ]
   css(`
       .myClass { color: ${mycolor[1]}; }
   `)

If a rule already exists, it will be overwritten by the new definition. Results are immediately shown by the browser. Definitions with css() work like any other CSS you provide with static definitions, they just are added from within Javascript. This makes it easy to control CSS programmatically. css can be used anywhere and anytime in the script. New css-rules will become active immediately and might even be changed as shown in the example below:

    const { button } = van.tags
    const { add, css } = van
        add(document.body,
        button({onclick: () => css(".class1 {background-color: red;}")},"set class1 red"),
        button({onclick: () => css(".class1 {background-color: green;}")},"set class1 green")
    );

!Attention:: css() adds new rules to the first stylesheet (window.document.styleSheets[0]). If the first stylesheet was loaded from an external source, this may cause CORS errors. For more information see here and here. Always add a local CSS-file first, as the dynamic rules are included in the first style sheet.

Support

If you need support, please use the Discussions page.