Standard Web Component wrapping the js-datapicker library

wc-date-picker.js

// WebComponent date-picker, a wrapper for js-datepicker
class DatePicker extends HTMLElement {
    constructor() {
        super();
    }

    connectedCallback() {
        // Load the js-datepicker once
        if (typeof datepicker === 'undefined') { // "datepicker" does not exists 
            if (!window.jsDatepicker) {          // not already running (no other instance of the same WC)
                const script = document.createElement('script');
                script.src = "https://unpkg.com/js-datepicker";
                document.body.appendChild(script);
                script.addEventListener('load', () => {
                    window.jsDatepicker = 'avail';  // when script is fully loaded, mark it "available"
                });

                const link = document.createElement('link');
                link.rel = "stylesheet";
                link.href = "https://unpkg.com/js-datepicker/dist/datepicker.min.css";
                document.head.appendChild(link); // in main doc, to be able to change styles

                window.jsDatepicker = 'loading';
            }
        } else if (typeof datepicker !== 'function') { // "datepicker" exists but it is not a function
            alert("Name conflict: js-datepicker not loadable, the name 'datepicker' is already in use");
            return;
        } else { // "datepicker" exists and it is a function: therefore js-datepicker is available
            window.jsDatepicker = 'avail';
        }

        // Create the input field (no Shadow DOM)
        const fldId = "input_" + this.id;
        this.innerHTML = `<input id="${fldId}" type="text">`;

        // Get the config options from the data-option attribute
        var options = {};
        var wc = this;
        if (typeof wc.dataset.options === 'string') {
            options = wc.getObjectFromString(wc.dataset.options);
        }

        // Wait till the script is loaded
        var interval = setInterval(() => {
            if (window.jsDatepicker === 'avail' && typeof datepicker === 'function') {
                clearInterval(interval);    // remove the timer
                wc.datepicker = datepicker(`#${fldId}`, options); // initialize and save object as a property
            }
        }, 20)
    }

    disconnectedCallback() {
    }

    static get observedAttributes() {
        return []; // no observed attributes for now
    }

    attributeChangedCallback(name, oldValue, newValue) {
    }

    // Utility function to transform a JS literal into a JS object
    getObjectFromString(string) {
        const getobj = new Function(`return ${string}`);
        try {
            const obj = getobj();
            return obj;
        } catch (error) {
            throw ('Invalid JavaScript object string: ' + string);
        }
    }
}

customElements.define('date-picker', DatePicker);