yeahjs

A tiny, modern, fast implementation of EJS (Embedded JavaScript Templates). A nearly drop-in replacement for ejs with a few intentional limitations.

Example

<ul>
<% for (let word of locals.items) { -%>
  <li><%= word %></li>
<% } -%>
</ul>

import {compile} from 'yeahjs';

const template = compile(ejs);
const output = template({items: ['flour', 'water', 'salt']});

<ul>
  <li>flour</li>
  <li>water</li>
  <li>salt</li>
</ul>

Compared to ejs

There are a few key differences that allow yeahjs to be so small and fast:

• Strict mode only (no with keyword in compiled functions).
• Only static path includes (include('header.ejs'), but not include(dir + file)).
• File handling not included — provide it with read and resolve options (see example).

Otherwise yeahjs produces identical output to ejs.

Strict mode only

The with keyword has a very significant impact on performance in JavaScript, in addition to introducing hard to debug issues. Limiting yeahjs to strict mode makes sure it's always as fast and predictable as possible.

Static path includes

Static path includes make sure yeahjs can fully compile templates with includes at compile time, avoiding lazy compilation during template evaluation. This makes evaluation faster and more predictable.

Custom file handling

Not including any file-system-specific code makes yeahjs environment-agnostic, having the same bundle for both Node and the browsers and giving full control over how includes get read and resolved.

Usage

import {compile} from 'yeahjs';

const template = compile(ejs, options);

Returns a function of the form (data) => content. Options:

• localsName: the namespace to use for accessing template data (locals by default for <%= locals.foo %>).
• locals: an array of variables to access directly (e.g. ['foo'] will allow <%= foo %> instead of <%= locals.foo %>).
• context: an object to use as this in templates (null by default).
• escape: a custom escaping function for values inside <%= ... %> (escapes XML by default).
• async: if true, generates an async function to make it possible to use await inside templates (false by default).
• filename: the file name of the template if present (used for resolving includes).
• read: a function of the form (filename) => content for reading includes (e.g. from file system in Node).
• resolve: a function of the form (parentPath, includePath) => path for resolving include paths.
• cache: an object to cache compiled includes in for faster compilation; reuse between compile runs for best performance ({} by default).

EJS cheatsheet

• <%= value %>: output the value (escaped).
• <%- value %>: output the value (raw).
• <% code %>: use arbitrary JavaScript.
• <%_ code %>: use arbitrary JavaScript and strip whitespace on the same line before the tag.
• ... _%>: strip whitespace and a single line break on the same line after the tag.
• ... -%>: strip a single line break immediately after the tag.
• <%%, %%>: output literal <% or %>.
• <%# comment %>: comment (ignored).
• <%- include('path/to/template.ejs', {foo: bar}) %>: include another template, optionally passing data.

File handling

An example of using read, resolve and filename options in Node.js to process includes:

import {readFileSync} from 'fs';
import {join, dirname} from 'path';

const template = yeahjs.compile(`<%- include('../bar.html') %>`, {
    filename: 'foo/foo.html',
    resolve: (parent, filename) => join(dirname(parent), filename),
    read: filename => readFileSync(filename, 'utf8')
});