Helpers
There are many Reaction-specific Template helpers available in the core/modules/client/helpers folder.
Meteor Template helper docs:
You can define helpers and event maps on Template.body just like on any Template.myTemplate object. Helpers on Template.body are only available in the
<body>tags of your app. To register a global helper, use Template.registerHelper. Event maps on Template.body don't apply to elements added to the body via Blaze.render, jQuery, or the DOM API, or to the body element itself. To handle events on the body, window, or document, use jQuery or the DOM API.
See a list of Helper methods in the API Docs: Helpers.