Extending Typescript interface functionality

I need help with extending a TypeScript interface where the property 'value' in the class is not being recognized as an array!

Here is the code snippet:

export class InListFilter<T, D=T[]> extends BaseFilter<T, D> {

    constructor(props: Partial<BaseFilter<T>>) {
        super(props);
    }

    getValue(): string {

        let s: string[] = [];

        if (this.value && this.value.length) {  // <- Property length does not exist on type D
            for (let v of this.value) {
                v = this.getValueParsed(v);
                s.push(this.enquoted ? `'${v}'` : `${v}`);
            }
        }

        return s && s.length ? s.join(',') : '';
    }

    render(): string {

        let s: string = '';

        if (!this.field || !this.hasValue()) {
            return s;
        }

        return `(${this.field} IN (${this.getValue()}))`;
    }
}

Thank you for your assistance!

Answer №1

According to the details provided on generics constraints in TypeScript Documentation:

The constraint can be indicated using the extends keyword.

In your particular example, the constraint would look like this:

export class InListFilter<T, D extends T[]> extends BaseFilter<T, D> {

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