Override Lodash Template Delimiters Globally

This article explains how to change the default ERB-style delimiters in Lodash's _.template function globally across your application. By modifying the _.templateSettings object, you can replace the standard <% %> tags with alternative syntaxes, such as Mustache-style {{ }} curly braces, ensuring consistent template parsing across all compile calls without passing custom settings every time.

Understanding _.templateSettings

Lodash controls template parsing rules via the _.templateSettings object. By default, it uses regular expressions that mimic ERB/EJS syntax:

• interpolate: Matches expressions to be printed verbatim (default: <%=([\s\S]+?)%>).
• escape: Matches expressions to be HTML-escaped and printed (default: <%-([\s\S]+?)%>).
• evaluate: Matches code blocks to be evaluated (default: <%([\s\S]+?)%>).

Because _.template references this object directly when no local options are provided, modifying _.templateSettings applies the changes to all subsequent _.template invocations.

Modifying Delimiters Globally

To apply new delimiters globally, import Lodash and update the regular expression properties on _.templateSettings before compiling any templates.

Example: Switching to Mustache/Handlebars Syntax

If you prefer {{ value }} for interpolation and {{{ value }}} or {{- value }} for escaping, you can configure the regular expressions as follows:

const _ = require('lodash');

// Configure global delimiters
_.templateSettings.interpolate = /{{([\s\S]+?)}}/g;
_.templateSettings.escape = /{{-([\s\S]+?)}}/g;
_.templateSettings.evaluate = /{%(.*?)/g;

// Compiling without custom options now uses the global settings
const compiled = _.template('Hello {{ user }}!');

console.log(compiled({ user: 'Alex' })); 
// Output: Hello Alex!

Order of Matching Precedence

When defining custom regular expressions for interpolate, escape, and evaluate, ensure that more specific patterns do not conflict with broader ones.

For instance, if {{- expression }} is used for escaping and {{ expression }} for interpolation, make sure the expressions are strict enough so that interpolate does not inadvertently consume the prefix intended for escape. Lodash internally checks escape, then interpolate, and then evaluate.

Resetting Delimiters

If you need to revert to the standard ERB-style delimiters later in execution, assign the original regular expressions back to _.templateSettings:

_.templateSettings.interpolate = /<%=([\s\S]+?)%>/g;
_.templateSettings.escape = /<%-([\s\S]+?)%>/g;
_.templateSettings.evaluate = /<%([\s\S]+?)%>/g;