DefaultOptionsExample.ts

interface IXOptions {
    a?: string,
    b?: any,
    c?: number
}

const XDefaults: IXOptions = {
    a: "default",
    b: null,
    c: 1
}

export class ClassX {
    private options: IXOptions;

    constructor(XOptions: IXOptions) {
        this.options = { ...XDefaults, ...XOptions };
    }

    public printOptions(): void {
        console.log(this.options.a);
        console.log(this.options.b);
        console.log(this.options.c);
    }
}