Why Am I Getting an 'Underscore Template Variable Not Defined' Error in Backbone.js?

Underscore Template Variable Not Defined Error Resolved

In Backbone.js, using Underscore templates to dynamically generate HTML is common, but earlier code snippets may encounter "variable not defined" errors. This article explains why this occurs and how to resolve it.

The Issue

In the past, Underscore templates could be parsed and filled in a single step using the following syntax:

var html = _.template(template_string, data);

The Change

However, Underscore versions 1.7.0 and above introduced the concept of template options, which must be explicitly provided as the second argument to _.template(). These options allow for fine-grained control over template behavior.

The Solution

To compile and execute Underscore templates correctly, follow these steps:

1. Compile the template using _.template(template_string).
2. Execute the returned function with the data to fill in the template.

This can be represented as:

var tmpl = _.template(template_string);
var html = tmpl(data);

Example

Consider the following code snippet, which shows how to implement templates with Airbnb's Vacation Rentals dataset:

var V = Backbone.View.extend({
  el: 'body',
  render: function() {
    var data = [
      {
        id: 1,
        lat: -27,
        lon: 153
      },
      {
        id: 2,
        lat: -33,
        lon: 151
      }
    ];
    var tmpl = _.template('

. ,

'); var html = data.map(tmpl).join(''); this.$el.html(html); return this; } }); var v = new V(); v.render();

By following the correct template syntax, you can effectively use Underscore templates in your Backbone.js applications.

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