Extending JavaScript

To extend JavaScript classes from other modules, use the extend key in the Webpack configuration. Define the path to the class being extended using nested keys.

extend:
  vendor/some-module/common/BaseClass:
    my-extended-class: vendor/my-module/extend/BaseClassExtend

The extended class should be exported as a function that takes the base class as an argument and returns a new class that extends it. You can extend multiple classes without limitation.
Example:

export function extend(BaseClass) {
    return class extends BaseClass {
        anyMethod(args) {
            super.anyMethod(args);
            // do more things
        }
 
        newMethod(args) {
            // do something new
        }
    }
}

Extending or Overwriting Properties

When extending a class, the parent constructor runs first, followed by the child constructor if it exists. If the parent constructor calls methods, they will use its properties, which may not always be ideal. To handle this, use the extendProperties method, available in all Lightna module classes.

export class BaseClass {  
    static MY_STATIC_PROPERTY = 'static-property-value';
    myProperty = 'regular-property-value';
    myClasses = {
        loading: 'loading',
        disabled: 'btn-disabled',
    };
 
    constructor() { 
        this.extendProperties(); 
    }
 
    extendProperties() { 
    } 
}

In the extended class, override the extendProperties method. Call the parent method first, then modify or add properties as needed.

export function extend(BaseClass) {
    return class extends BaseClass {
        extendProperties() {
            super.extendProperties();
            const parentClasses = this.myClasses;
            this.myClasses = {
                ...parentClasses,
                new: 'new-class',
            };
 
            BaseClass.MY_STATIC_PROPERTY = 'new-static-property-value';
        }
    }
}

Planned

A future update will allow the compiler to detect incompatibilities with the base class. Extensions will need to declare all properties and methods they use, helping identify issues when updating base modules.