Validating template variables in JavaScript-Collection of common programming errors

I suggest writing a function to take your template context object and prepare it for rendering. These are sometimes called presenter functions and/or the presenter pattern. You would use this from your node.js routing function before your render the template. This function could replace null/undefined with empty string and also detect objects whose toString is “[Object object]” or otherwise undesired and replace them with empty string as well. It is easy to write unit tests for this and will prevent you from having to duplicate logic in many templates. This function should recursively walk an entire object graph or array of object graphs.

You may also want other functionality like abbreviating abnormally long strings. For example, if someone accidentally pastes in a bunch of garbage into the “firstName” field of your user object and this is over some sane limit of say 100 characters, your presenter function could truncate it and append an ellipsis. Just another example of this data cleanup or “presentation” type logic.

Otherwise, you need expressions like in your ejs templates which will cause lots of boilerplate code duplication.

Here’s a first-cut working jsfiddle implementation (uses underscore.js).

function sanitize(context) {
    if (Array.isArray(context)) {
      return _.map(context, sanitize);
    }
    _.each(context, function (value, key) {
        if (value === null) {
          context[key] = "";
          return;
        }

        switch (typeof value) {
          case "object":
            context[key] = sanitize(value);
            break;
          case "number":
            //No-op
            break;
          case "boolean":
            //No-op
            break;
          default:
            context[key] = value || ""; //handles undefined
        }                
    });
    return context;
}

Originally posted 2013-11-09 22:56:46.