Which JavaScript Libraries Work with Lightning Locker?

Question

Many components seem to function correctly with external libraries until Lightning Locker Service is enabled, at which point issues may arise. Which JavaScript libraries are known to work with Locker Service enabled, and where can I find a reliable source to verify compatibility?

Answer

Many JavaScript libraries may initially seem to function properly in Lightning components, but when Lightning Locker Service is enabled, issues can arise due to its strict security policies. Locker Service enforces ECMAScript 5 strict mode, restricts access to the global scope, and applies various security constraints to prevent cross-component access and DOM manipulation that could introduce vulnerabilities.

Libraries Known to Work with Locker Service

Salesforce has tested and confirmed that certain libraries work correctly with Locker Service enabled. However, libraries that do not support strict mode will not work. Below is a list of libraries known to be compatible:

|-- Libraries Known to Work ---|
|----- with Locker Service ------|
-------------------------------------------
| Library         | Version                 |
-------------------------------------------
| React          | 0.14.8                   |
| ChartJS        | 2.1.4                     |
| D3            | 4.4.0                     |
| RxJS           | Latest as of 12/5/16     |
| Leaflet        | 0.7.7 and 1.0.2          |
| Numeral.js     | 2.1.4                     |
| Underscore.js  | 1.8.3                     |
| FullCalendar   | 3.1.0                     |
| Gauge.js       | 1.2.1                     |
| jQuery        | 2.2.2 and 2.2.4           |
| jQuery UI     | 1.11.4                    |
| DataTables    | 1.10.12                   |
| Select2        | 4.0.3                     |
-------------------------------------------

Understanding Why Some Libraries Work While Others Do Not

1. Strict Mode Requirement:

Locker Service enforces strict mode, which means that any library using outdated JavaScript practices, such as implicit global variables or modifying window directly, will likely break. Libraries that are written with modern JavaScript best practices and explicitly support strict mode are more likely to be compatible.

2. Limited Access to Global Scope:
In standard JavaScript execution, libraries often modify global objects such as window or document. However, Locker Service prevents direct access to these global objects. Libraries that depend on modifying these objects (for example, by injecting global variables or manipulating global event handlers) will likely fail.

3. Secure DOM Access:
Locker Service ensures that Lightning components cannot access or modify other components’ DOM elements outside their own namespace. This means that any library that attempts to traverse the DOM tree beyond its own component (e.g., document.querySelector('some-element')) might not work as expected.

Best Practices When Using External Libraries with Locker Service

If you plan to use an external library in your Lightning components, follow these guidelines to ensure compatibility with Locker Service:

1. Load Libraries as Static Resources:
Upload the library as a Static Resource in Salesforce and then load it using loadScript() in LWC or Aura components.

Example for LWC:

import { LightningElement } from 'lwc';
import { loadScript } from 'lightning/platformResourceLoader';
import myLibrary from '@salesforce/resourceUrl/myLibrary';

export default class MyComponent extends LightningElement {
    renderedCallback() {
        loadScript(this, myLibrary)
            .then(() => {
                console.log('Library loaded successfully');
            })
            .catch(error => {
                console.error('Error loading library:', error);
            });
    }
}

2. Avoid Using jQuery for UI Manipulation:
Although jQuery (versions 2.2.2 and 2.2.4) is known to work with Locker Service, it should not be used for UI modifications inside Lightning components. Salesforce strongly recommends using the Lightning Design System (LDS) instead of jQuery for styling and UI interactions.

Example of LDS usage instead of jQuery:

<lightning-button label="Click Me" onclick={handleClick}></lightning-button>

Instead of:

$('button').on('click', function() { alert('Clicked!'); });

3. Ensure the Library Does Not Conflict with Locker Service Restrictions:

• No direct window or document access (use scoped variables instead).
• No reliance on eval() or Function() constructor, as they are blocked.
• No usage of outdated JavaScript practices that are restricted in strict mode.

Where to Find More Information?

Salesforce continuously updates its list of compatible libraries. The most recent official list was published in a Salesforce Developer Blog post titled “LockerService and Lightning Container Component: Securely Using Third-Party Libraries in Lightning Components.”

To ensure the latest compatibility updates, you can:

1. Check Salesforce Developer Blog for any new updates.
2. Refer to Salesforce Documentation on Locker Service security guidelines.
3. Test the library yourself by loading it in a component with Locker Service enabled.

Not all JavaScript libraries will work with Locker Service, primarily due to strict mode enforcement, limited global scope access, and secure DOM policies. If you need to use an external library, check its compatibility with Locker Service, load it as a Static Resource, and ensure it adheres to modern JavaScript standards. When possible, prefer native Lightning Web Components (LWC) and Lightning Design System (LDS) over external libraries for better performance and security.

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