DocumentFragment missing getElementById()

[arjunyel]

TypeScript Version: 2.2.1

Code

class FragmentBug extends HTMLElement{
    constructor(){
        super();
        const shadowRoot = this.attachShadow({mode: 'open'});
        shadowRoot.innerHTML = `
            <div id="byid"></div>
        `;
        const p = document.createElement("p");
        this.shadowRoot.getElementById("byid").appendChild(p);
        /*ERROR: Property 'getElementById' does not exist on type 'ShadowRoot'.*/
     }
};
customElements.define('fragment-bug', FragmentBug);

Expected behavior:

ShadowRoot inherits getElementById() from DocumentFragment, which returns an Element, and appends a <p> tag to the <div>

MDN DocumentFragment

Actual behavior:

error TS2339: Property 'getElementById' does not exist on type 'ShadowRoot'.