ember-template-lint

What is ember-template-lint?

ember-template-lint is a linting tool for Ember.js templates. It helps developers maintain consistent coding styles, catch potential errors, and enforce best practices in Handlebars templates.

What are ember-template-lint's main functionalities?

Linting Templates

This feature allows you to lint your Handlebars templates to ensure they follow specific rules. For example, the 'no-bare-strings' rule prevents the use of bare strings in templates, encouraging the use of translation helpers instead.

module.exports = { 'no-bare-strings': true };

Custom Rules

You can define custom linting rules to enforce specific coding standards within your project. In this example, the 'no-inline-styles' rule is set to 'error' severity, which will flag any inline styles in templates as errors.

module.exports = { rules: { 'no-inline-styles': { severity: 'error' } } };

Configuration File

You can extend from predefined configurations to quickly set up linting rules. The 'recommended' configuration includes a set of rules that are generally considered best practices for Ember.js templates.

module.exports = { extends: 'recommended' };

Other packages similar to ember-template-lint

eslint

ESLint is a widely-used linting tool for JavaScript. It helps developers find and fix problems in their JavaScript code. While ESLint focuses on JavaScript, ember-template-lint is specifically designed for Handlebars templates in Ember.js.

stylelint

Stylelint is a linter for CSS and other stylesheets. It helps enforce consistent conventions and avoid errors in stylesheets. Like ember-template-lint, it is highly configurable, but it focuses on styles rather than Handlebars templates.

ember-cli-template-lint

ember-cli-template-lint is an older package that integrates template linting into the Ember CLI build process. It has been largely superseded by ember-template-lint, which offers more features and better integration.

README

ember-template-lint

ember-template-lint will lint your template and return error results. This is commonly used through ember-cli-template-lint which adds failing lint tests for consuming ember-cli applications.

For example, given the rule bare-strings is enabled, this template would be in violation:

{{! app/components/my-thing/template.hbs }}
<div>A bare string</div>

When ran through the linter's verify method, we would have a single result indicating that the bare-strings rule found an error.

Install

To install ember-template-lint

npm install --save-dev ember-template-lint

Usage

Run templates through the linter's verify method like so:

var TemplateLinter = require('ember-template-lint');

var linter = new TemplateLinter();
var template = fs.readFileSync('some/path/to/template.hbs', { encoding: 'utf8' });
var results = linter.verify(template);

results will be an array of objects which have the following properties:

• rule - The name of the rule that triggered this warning/error.
• message - The message that should be output.
• line - The line on which the error occurred.
• column - The column on which the error occurred.
• moduleId - The module path for the file containing the error.
• source - The source that caused the error.
• fix - An object describing how to fix the error.

Configuration

Project Wide

You can turn on specific rules by toggling them in a .template-lintrc.js file at the base of your project:

module.exports = {
  extends: 'recommended',

  rules: {
    'bare-strings': true
  }
}

This extends from the builtin recommended configuration (lib/config/recommended.js), and also enables the bare-strings rule (see here).

Using this mechanism allows you to extend from the builtin, and modify specific rules as needed.

Some rules also allow setting additional configuration, for example if you would like to configure some "bare strings" that are allowed you might have:

module.exports = {
  rules: {
    'bare-strings': ['ZOMG THIS IS ALLOWED!!!!']
  }
};

Per Template

It is also possible to disable specific rules (or all rules) in a template itself:

{{! disable all rules for this template }}
<!-- template-lint disable=true -->

{{! disable specific rules for this template }}
<!-- template-lint bare-strings=false -->

It is not currently possible to change rule configuration in the template.

Configuration Keys

The following properties are allowed in the root of the .template-lintrc.js configuration file:

• rules -- This is an object containing rule specific configuration (see details for each rule below).
• extends -- This is a string that allows you to specify an internally curated list of rules (we suggest recommended here).
• pending -- An array of module id's that are still pending. The goal of this array is to allow incorporating template linting into an existing project, without changing every single template file. You can add all existing templates to this pending listing and slowly work through them, while at the same time ensuring that new templates added to the project pass all defined rules.

Rules

bare-strings

In order to be able to internationalize your application, you will need to avoid using plain strings in your templates. Instead, you would need to use a template helper specializing in translation (ember-i18n and ember-intl are great projects to use for this).

This rule forbids the following:

<h2>Some string here!</h2>

The following values are valid configuration:

• boolean -- true for enabled / false for disabled
• array -- an array of whitelisted strings
• object -- An object with the following keys:
  • whitelist -- An array of whitelisted strings
  • globalAttributes -- An array of attributes to check on every element.
  • elementAttributes -- An object whose keys are tag names and value is an array of attributes to check for that tag name.

When the config value of true is used the following configuration is used:

• whitelist - (),.&+-=*/#%!?:[]{}
• globalAttributes - title
• elementAttributes - { img: ['alt'], input: ['placeholder'] }

block-indentation

Good indentation is crucial for long term maintenance of templates. For example, having blocks misaligned is a common cause of logic errors...

This rule forbids the following examples:

  {{#each foo as |bar}}

    {{/each}}

  <div>
  <p>{{t "greeting"}}</p>
  </div>

<div>
  <p>{{t 'Stuff here!'}}</p></div>

The following values are valid configuration:

• boolean -- true indicates a 2 space indent, false indicates that the rule is disabled.
• numeric -- the number of spaces to require for indentation
• "tab" -- To indicate tab style indentation (1 char)

html-comments

Html comments in your templates will get compiled and rendered into the DOM at runtime. Instead you can annotate your templates using Handlebars comments, which will be stripped out when the template is compiled and have no effect at runtime.

This rule forbids the following:

<!-- comment goes here -->

but allows the following:

{{!-- comment goes here --}}

Html comments containing linting instructions such as:

<!-- template-lint bare-strings=false -->

are of course allowed (and since the linter strips them during processing, they will not get compiled and rendered into the DOM regardless of this rule).

triple-curlies

Usage of triple curly braces to allow raw HTML to be injected into the DOM is large vector for exploits of your application (especially when the raw HTML is user controllable ). Instead of using {{{foo}}}, you should use appropriate helpers or computed properties that return a SafeString (via Ember.String.htmlSafe generally) and ensure that user supplied data is properly escaped.

This rule forbids the following:

{{{foo}}}

nested-interactive

Usage of nested interactive content can lead to UX problems, accessibility problems, bugs and in some cases to DOM errors. You should not put interactive content elements nested inside other interactive content elements. Instead using nested interactive content elements you should separate them and put them one after the other.

This rule forbids the following:

<button type="button">
  Click here and <a href="/">go to home here</a>
</button>

The following values are valid configuration:

• boolean -- true indicates all whitelist test will run, false indicates that the rule is disabled.
• object - Containing the following values:
  • ignoredTags - An array of element tag names that should be whitelisted. Default to [].
  • ignoreTabindex - When true tabindex will be ignored. Defaults to false.
  • ignoreUsemapAttribute - When true ignores the usemap attribute on img and object elements. Defaults false.
  • additionalInteractiveTags - An array of element tag names that should also be considered as interactive. Defaults to [].'

self-closing-void-elements

HTML has no self-closing tags. The HTML 5 parser will ignore self-closing tag in the case of void elements (tags that shouldn't have a closing tag). Although the parser will ignore it's unnecessary and can lead to confusing with SVG/XML code.

This rule forbids the following:

<img src="http://emberjs.com/images/ember-logo.svg" alt="ember" />
<hr/>

Instead, you should write the template as:

<img src="http://emberjs.com/images/ember-logo.svg" alt="ember">
<hr>

The following values are valid configuration:

• boolean -- true for enabled / false for disabled

img-alt-attributes

An <img> without an alt attribute is essentially invisible to assistive technology (i.e. screen readers). In order to ensure that screen readers can provide useful information, we need to ensure that all <img> elements have an alt specified. See WCAG Suggestion H37.

The rule forbids the following:

<img src="rwjblue.png">

Instead, you should write the template as:

<img src="rwjblue.png" alt="picture of Robert Jackson">

The following values are valid configuration:

• boolean -- true for enabled / false for disabled

link-rel-noopener

When you want to link in your app to some external page it is very common to use <a href="url" target="_blank"></a> to make the browser open this link in a new tab. However, this practice has performance problems (see https://jakearchibald.com/2016/performance-benefits-of-rel-noopener/) and also opens a door to some security attacks because the opened page can redirect the opener app to somewhere to a malicious clone to perform phishing on your users.

To avoid those two problems, this rule forbids the following:

<a href="https://i.seem.secure.com" target="_blank">I'm a bait</a>

Instead, you should write the template as:

<a href="https://i.seem.secure.com" target="_blank" rel="noopener">I'm a bait</a>

The following values are valid configuration:

• boolean -- true for enabled / false for disabled

invalid-interactive

Adding interactivity to an element that is not naturally interactive content leads to a very poor experience for users of assistive technology (i.e. screen readers). In order to ensure that screen readers can provide useful information to their users, we should add an appropriate role attribute when the underlying element would not have made that role obvious.

This rule forbids the following:

<div {{action 'foo'}}></div>

Instead, you should add a role to the element in question so that the A/T is aware that it is interactive:

<div role="button" {{action "foo"}}></div>

The following values are valid configuration (same as the nested-interactive rule above):

• boolean -- true indicates all whitelist test will run, false indicates that the rule is disabled.
• object - Containing the following values:
  • ignoredTags - An array of element tag names that should be whitelisted. Default to [].
  • ignoreTabindex - When true tabindex will be ignored. Defaults to false.
  • ignoreUsemapAttribute - When true ignores the usemap attribute on img and object elements. Defaults false.
  • additionalInteractiveTags - An array of element tag names that should also be considered as interactive. Defaults to [].'

inline-link-to

Ember's link-to component has both an inline form and a block form. This rule forbids the inline form.

Forbidden (inline form):

{{link-to 'Link text' 'routeName' prop1 prop2}}

Allowed (block form):

{{#link-to 'routeName' prop1 prop2}}Link text{{/link-to}}

The block form is a little longer but has advantages over the inline form:

• It maps closer to the use of HTML anchor tags which wrap their inner content.
• It provides an obvious way for developers to put nested markup and components inside of their link.
• The block form's argument order is more direct: "link to route". The inline form's argument order is somewhat ambiguous (link text then link target). This is opposite of the order in HTML (href then link text).

This rule is configured with one boolean value:

• boolean -- true for enabled / false for disabled

style-concatentation

Ember has a runtime warning that says "Binding style attributes may introduce cross-site scripting vulnerabilities." It can only be avoided by always marking the bound value with Ember.String.htmlSafe. While we can't detect statically if you're always providing a safe string, we can detect cases common where it's impossible that you're doing so. For example,

<div style="background-style: url({{url}})">

is never safe because the implied string concatentation does not propagate htmlSafe. Any use of quotes is therefore forbidden. This is forbidden:

<div style="{{make-background url}}">

whereas this is allowed:

<div style={{make-background url}}>

Deprecations

deprecated-each-syntax

In Ember 2.0, support for using the in form of the {{#each}} helper has been removed.

For example, this rule forbids the following:

{{#each post in posts}}
  <li>{{post.name}}</li>
{{/each}}

Instead, you should write the template as:

{{#each posts as |post|}}
  <li>{{post.name}}</li>
{{/each}}

More information is available at the Deprecation Guide.

Contributing

A few ideas for where to take this in the future:

• The list of rules should be configurable
• This addon should use a test printer shared with jshint, eslint and jscs addons
• A command-line version of the linter should be provided so IDEs and editors can provide feedback to devs during development

Installation

• git clone this repository
• npm install

Running Tests

• npm test

Changelog

v0.5.16

• Fix issue with link-rel-noopener rule when using properly with a listing (i.e. rel="noopener noreferrer").
• Add inline-link-to rule to prevent usage of inline {{link-to.
• Add style-concatenation rule. This prevents the usage of <div style="{{make-background url}}"> (quoted value with any dynamic segments) but allows <div style={{make-background url}}>.