Handlebars

Handlebars is a JavaScript templating engine based on the Mustache template language. It enables the creation of semantic templates that render data into HTML or other text formats, emphasizing a separation between presentation and application logic. Handlebars templates are designed to be readable and maintainable, with the rendering performed by a runtime that injects data into the template.

The template syntax centers on double curly braces for expressions and supports a range of features. Variables are inserted with {{name}}, while block expressions enable logic and iteration, such as {{#if condition}}...{{/if}} and {{#each items}}...{{/each}}. Built-in helpers provide common functionality (for example, if, unless, each, with, and log), and developers can register custom helpers to implement additional logic or formatting. Partials allow reusable template fragments, promoting modular design and reuse.

In practice, Handlebars templates can be precompiled into JavaScript functions for faster rendering, or compiled on demand at runtime. The engine is framework-agnostic and can be used in client-side web applications, server-side rendering with Node.js, and various environments. It has historically been associated with Ember.js and other JavaScript ecosystems, where its logic-light approach complements declarative templates while still enabling custom behavior through helpers.

History and status: Handlebars originated as an extension of Mustache to add helpers and block expressions while preserving Mustache’s minimal logic approach. It has been maintained as an open-source project with broad ecosystem support, including different runtimes and ports in other languages. See also: Mustache, Ember.js, templating engines.