A simple clientside templating langauge

Paul Kinlan
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In a recent project, I wanted a simple way to bind some JSON data to a DOM element without importing any libraries and I think I came up with a pretty neat solution (in my eyes) that fit all my needs for the project.

The solution encodes templating instructions inside DOM data attributes named data-bind-*, which are accessible on the DOM element in the dataset property and it just so happens to camel-case the attributes automatically (i.e, to set innerText you would have an attribute data-bind_inner-text - note the hyphen).

Here is a sample template from the project:

<template id="itemTemplate">
  <div class="item new" data-bind_id="guid" id="">
    <h3><span data-bind_inner-text="title"></span></h3>
    <p class="description" data-bind_inner-text="content:encoded|description"></p>
    <div>
      <a data-bind_href="link" data-bind_inner-text="pubDate" data-bind_title="title" href="" title=""></a>
      <svg class="share" url="" title="" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg" width="24" height="24">
        <path fill="none" d="M0 0h24v24H0z"></path><path d="M18 16c-.8 0-1.4.4-2 .8l-7-4v-1.5l7-4c.5.4 1.2.7 2 .7 1.7 0 3-1.3 3-3s-1.3-3-3-3-3 1.3-3 3v.7l-7 4C7.5 9.4 6.8 9 6 9c-1.7 0-3 1.3-3 3s1.3 3 3 3c.8 0 1.5-.3 2-.8l7.2 4.2v.6c0 1.6 1.2 3 2.8 3 1.6 0 3-1.4 3-3s-1.4-3-3-3z"></path>
      </svg>
    </div>
  </div>
</template>

As you can see, we use the <template> element to ensure that we can keep our HTML in the DOM and to keep it inert (this really improves the authoring experience). Note, it doesn’t have to be a template element, it can take anything that is inside the DOM.

To map the above DOM into an actual element with all the live data applied to it, I use the following basic algorithm:

  1. Clone the element to bind data on to.
  2. Iterate across the elements and for each element:
    1. Check to see if it has an attribute of the form data-bind_
    2. Get the keys to lookup on the data separated by a “|”
    3. Map the first found key’s value from the input data directly to the node’s attribute defined by data-bind_
  3. Return the new node.

The code for this is pretty simple, if a tad terse.

const applyTemplate = (templateElement, data) => {
  const element = templateElement.content.cloneNode(true);    
  const treeWalker = document.createTreeWalker(element, NodeFilter.SHOW_ELEMENT, () => NodeFilter.FILTER_ACCEPT);

  while(treeWalker.nextNode()) {
    const node = treeWalker.currentNode;
    for(let bindAttr in node.dataset) {
      let isBindableAttr = (bindAttr.indexOf('bind_') == 0) ? true : false;
      if(isBindableAttr) {
        let dataKeyString = node.dataset[bindAttr];
        let dataKeys = dataKeyString.split("|");
        let bindKey = bindAttr.substr(5);
        for(let dataKey of dataKeys) {
          if(dataKey in data && data[dataKey] !== "") {
            node[bindKey] = data[dataKey];
            break;
          }
        }
      }
    }
  }

  return element;
}

I don’t expect anyone to use this, but I wanted to show how you can build a data binding tool for simple tasks without having to resort to a full library or framework.

Paul Kinlan

Trying to make the web and developers better.

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