How can we utilize attributeChangedCallback in TypeScript?

When looking at this particular guide, the implementation of attributeChangedCallback is demonstrated as follows:

// attribute change
attributeChangedCallback(property, oldValue, newValue) {

  if (oldValue === newValue) return;
  this[ property ] = newValue;

}

My attempt to convert it to Typescript has resulted in the following code snippet:

// attribute change
attributeChangedCallback(property:keyof HelloWorldComponent, oldValue:any, newValue:any) {
    if (oldValue === newValue) return;
    this[ property ] = newValue;  
  }  
}

Despite my efforts, I am now encountering the error messages shown below:

Cannot assign to 'ATTRIBUTE_NODE' because it is a read-only property.ts(2540)
Cannot assign to 'CDATA_SECTION_NODE' because it is a read-only property.ts(2540)
Cannot assign to 'COMMENT_NODE' because it is a read-only property.ts(2540)
Cannot assign to 'DOCUMENT_FRAGMENT_NODE' because it is a read-only property.ts(2540)
Cannot assign to 'DOCUMENT_NODE' because it is a read-only property.ts(2540)

Any insights or suggestions on how to address this issue?

Answer №1

It appears that you are attempting to modify properties that are marked as read-only, and TypeScript automatically assumes a type that includes read-only properties when it cannot accurately deduce the type of the property parameter

Here is an improved solution:

class GreetingsComponent extends HTMLElement {
  
  private greeting: string | null = null;
  private message: string | null = null;

    attributeChangedCallback(attribute: string, oldVal: string | null, newVal: string | null) {
    if (oldVal === newVal) return;
    
    switch (attribute) {
      case 'greeting':
        this.greeting = newVal;
        break;
      case 'message':
        this.message = newVal;
        break;
      // Manage other attributes as necessary
      default:
        throw new Error(`Unrecognized attribute: ${attribute}`);
    }
  }
}

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