test.ts

import * as d3 from "d3";

export default class Chart {
    
    private elements: Array<Element>;

    constructor(target: string|Element|NodeList) {
        this.elements = Chart.parseTarget(target);
    }

    private static parseTarget(target: string|Element|NodeList): Array<Element> {
        if (typeof target === "string") return Array.from(document.querySelectorAll(target));
        if (typeof target === "NodeList") return Array.from(target);
        if (target instanceof Element) return [target];
        throw new TypeError();
    }
}