All files / src/custom-element/mixins AttributeChangeHandlerMixin.ts

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import { attributeMarkerPrefix } from "../../renderer/createTemplate";
import valueConverter from "../helpers/valueConverter";
import { CustomElementPropertyMetadata } from "../interfaces";
import PropertyMetadataInitializerMixin from "./PropertyMetadataInitializerMixin";
 
const AttributeChangeHandlerMixin = Base =>
 
    class AttributeChangeHandler extends PropertyMetadataInitializerMixin(Base) { // This mixin requires an implementation of setProperty
 
        /**
         * The properties of the instance
         */
        private _properties: Record<string, any> = {};
 
        /**
         * Map of the metadata of the changed properties so that the "change" method can be called after the update of the DOM
         */
        private _changedProperties: Map<string, CustomElementPropertyMetadata> = new Map<string, CustomElementPropertyMetadata>();
 
        constructor() {
 
            super();
 
            this._initializePropertiesWithDefaultValues((this.constructor as any).metadata.properties);
        }
 
        /**
         * Initializes the properties that have a default value
         * @param propertiesMetadata 
         */
        private _initializePropertiesWithDefaultValues(propertiesMetadata: Map<string, CustomElementPropertyMetadata>) {
 
            for (const [name, property] of propertiesMetadata) {
 
                const {
                    value
                } = property;
 
                if (this._properties[name] === undefined &&
                    value !== undefined) {
 
                    this.setProperty(name, value);
                }
            }
        }
 
        connectedCallback() {
 
            super.connectedCallback?.();
 
            const {
                properties
            } = (this.constructor as any).metadata;
 
            this._validateRequiredProperties(properties);
        }
 
        // Without defining this method, the observedAttributes getter will not be called
        // Also no need to check that the property was configured because if it is not configured, 
        // it will not generate the observedAttribute and therefore this method won't be called for that attribute
        /**
         * Called when there is a change in an attribute
         * @param attributeName
         * @param oldValue 
         * @param newValue 
         */
        attributeChangedCallback(attributeName: string, oldValue: string | null, newValue: string | null) {
 
            super.attributeChangedCallback?.(attributeName, oldValue, newValue);
 
            this._setAttribute(attributeName, newValue);
        }
 
        /**
         * Validates that all the required properties have been set
         * @param propertiesMetadata 
         */
        private _validateRequiredProperties(propertiesMetadata: Map<string, CustomElementPropertyMetadata>) {
 
            const missingValueAttributes: string[] = [];
 
            for (const [, property] of propertiesMetadata) {
 
                const {
                    required,
                    attribute
                } = property;
 
                if (required === true &&
                    this.attributes[attribute] === undefined) { // The attribute for that property has not been set
 
                    missingValueAttributes.push(attribute);
                }
            }
 
            if (missingValueAttributes.length > 0) {
 
                throw Error(`The attributes: [${missingValueAttributes.join(', ')}] must have a value`)
            }
        }
 
        // /**
        //  * Overrides the parent method to verify that it is accessing a configured property
        //  * @param attribute 
        //  * @param value 
        //  */
        // setAttribute(attribute: string, value: any) {
 
        //     // Verify that the property is one of the configured in the custom element
        //     if ((this.constructor as any)._propertiesByAttribute[attribute] === undefined &&
        //         !(this.constructor as any).metadata.htmlElementProperties.has(attribute)) {
 
        //         throw Error(`There is no configured property for attribute: '${attribute}' in type: '${this.constructor.name}'`)
        //     }
 
        //     super.setAttribute(attribute, value);
        // }
 
        private _setAttribute(attribute: string, value: any): boolean {
 
            if (value.startsWith(attributeMarkerPrefix)) { // Coming from a template ... ignore
 
                return false;
            }
    
            // Verify that the property is one of the configured in the custom element
            let propertyMetadata = (this.constructor as any).metadata.propertiesByAttribute.get(attribute);
 
            const {
                name,
                type
            } = propertyMetadata;
 
            value = valueConverter.toProperty(value, type); // Convert from the value returned by the parameter
 
            return this.setProperty(name, value);           
        }
 
        protected setProperty(name: string, value: any): boolean {
 
            const oldValue = this._properties[name];
 
            if (oldValue === value) {
 
                return false;
            }
 
            if (typeof value === 'function') {
 
                this._properties[name] = (value as Function).bind(this);
            }
            else {
 
                this._properties[name] = value;
            }
 
            // Verify that the property is one of the configured in the custom element
            let propertyMetadata: CustomElementPropertyMetadata = (this.constructor as any).metadata.properties.get(name);
 
            const {
                attribute,
                reflect,
                //change We call change after the element was updated in the DOM
            } = propertyMetadata;
 
            const reflectOnAttribute = reflect === true ? attribute : undefined;
 
            if (reflectOnAttribute !== undefined) { // Synchronize with the attribute of the element
 
                value = valueConverter.toAttribute(value);
 
                if (value === '') {
 
                    this.removeAttribute(reflectOnAttribute);
                }
                else {
 
                    // This will trigger the attributeChangedCallback
                    this.setAttribute(reflectOnAttribute, value);
                }
 
            }
 
            this._changedProperties.set(name, (this.constructor as any).metadata.properties.get(name));
 
            return true;
        }
 
        protected callAttributesChange() {
 
            this._changedProperties.forEach((p, k) => {
 
                if (p.afterUpdate !== undefined) { // Call the change function if defined
 
                    p.afterUpdate.call(this);
                }
            });
        }
 
        protected clearChangedProperties() {
 
            this._changedProperties.clear();
        }
 
    }
 
export default AttributeChangeHandlerMixin;