How do you create custom HTML element?
Interviewer Expectations for this Question
01
Core Competency
Assesses fundamental understanding of JavaScript conventions, runtime behavior, and memory/performance considerations.
02
Evaluation Criteria
Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.
Comprehensive Model Answer
Verified Solution
The creation of custom HTML elements involves two main steps,
- Define your custom HTML element: First you need to define some custom class by extending HTMLElement class.
After that define your component properties (styles,text etc) using connectedCallback method.
Note: The browser exposes a function called customElements.define inorder to reuse the element.
class CustomElement extends HTMLElement {
connectedCallback() {
this.innerHTML = "This is a custom element";
}
}
customElements.define("custom-element", CustomElement);
- Use custom element just like other HTML element: Declare your custom element as a HTML tag.
<body>
<custom-element>
</body>
Candidate Response Strategy & Interview Tips
- Start with a concise one-sentence summary: Deliver a direct, confident answer first before expanding into nuances.
- Demonstrate real-world trade-offs: Discuss where this approach excels and when you would avoid it in production systems.
- Discuss complexity & edge cases: Proactively explain time/space complexity or boundary conditions (null values, scale limits).
- Prepare for interviewer follow-ups: Technical hiring panels frequently probe deeper into concurrency, backward compatibility, or alternative libraries.