Using an array of custom TypeScript types or objects as a property in Lit v2

Question

Using an array of custom TypeScript types or objects as a property in Lit v2

I am seeking to convert my existing JavaScript CustomElements/WebComponents (created with Lit v1 and later migrated to v2) into TypeScript.

For instance:

export class MyElement extends LitElement {
  ...
  @property({type: String})
  name = 'World';
  ...
}

... or you can check this example out: https://github.com/lit/lit-element-starter-ts/blob/main/src/my-element.ts#L37

Is there a way for me to declare a property as an array of my custom TypeScript classes?

For example, like this:

export class MyElement extends LitElement {
  ...
  @property({type: Array<MyCustomClass>})
  customClassArray = [];
  // or: customClassArray = [new MyCustomClass("foo")]; 
  ...
}

typescript lit-element lit

Answer 1

Answer №1

When working with Lit, the @property decorator plays a key role in creating reactive properties and ensuring that the attribute value is reflected accurately (especially if reflect: true is enabled). However, handling non-string values, such as numbers or booleans, can be tricky. Numbers need to be parsed correctly, and for booleans, the mere existence of the attribute indicates a value of true.

To tackle this issue, Lit introduces the concept of type, which allows you to specify the appropriate converter for attribute values. Think of it as specifying a type hint or conversion type for attribute/value transformations. For reference, you can check out Lit's default converter.

It is important to define your actual types in TypeScript when using Lit.

export class YourElement extends LitElement {
  @property({ type: Array })
  customClassArray = new Array<YourCustomClass>();
  // or: customClassArray = [new YourCustomClass()];
}

Answer 2

When working with Lit, the @property decorator plays a key role in creating reactive properties and ensuring that the attribute value is reflected accurately (especially if reflect: true is enabled). However, handling non-string values, such as numbers or booleans, can be tricky. Numbers need to be parsed correctly, and for booleans, the mere existence of the attribute indicates a value of true.

To tackle this issue, Lit introduces the concept of type, which allows you to specify the appropriate converter for attribute values. Think of it as specifying a type hint or conversion type for attribute/value transformations. For reference, you can check out Lit's default converter.

It is important to define your actual types in TypeScript when using Lit.

export class YourElement extends LitElement {
  @property({ type: Array })
  customClassArray = new Array<YourCustomClass>();
  // or: customClassArray = [new YourCustomClass()];
}

Answer 3

Answer №2

I have come up with a solution on my own that is quite similar to what @arshia11d suggested.

import { MyCustomClass } from './MyCustomClass';    

export class MyElement extends LitElement {
      @property({ type: Array }) //Array<MyCustomClass> throws ts(2303) error
      annotations: MyCustomClass[] = [];
    }

Here is the type definition:

export interface IMyCustomClass {
  label: string;
}

export class MyCustomClass implements IMyCustomClass {
  label: string;

  constructor(
    _label: string
  ) {
    this.label = _label;
  }
}

Answer 4

I have come up with a solution on my own that is quite similar to what @arshia11d suggested.

import { MyCustomClass } from './MyCustomClass';    

export class MyElement extends LitElement {
      @property({ type: Array }) //Array<MyCustomClass> throws ts(2303) error
      annotations: MyCustomClass[] = [];
    }

Here is the type definition:

export interface IMyCustomClass {
  label: string;
}

export class MyCustomClass implements IMyCustomClass {
  label: string;

  constructor(
    _label: string
  ) {
    this.label = _label;
  }
}

Using an array of custom TypeScript types or objects as a property in Lit v2

Answer №1

Answer №2

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