How do you make asynchronous HTTP request?
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
Browsers provide an XMLHttpRequest object which can be used to make asynchronous HTTP requests from JavaScript by passing the 3rd parameter as true.
function httpGetAsync(theUrl, callback) {
var xmlHttpReq = new XMLHttpRequest();
xmlHttpReq.onreadystatechange = function () {
if (xmlHttpReq.readyState == 4 && xmlHttpReq.status == 200)
callback(xmlHttpReq.responseText);
};
xmlHttpReq.open("GET", theUrl, true); // true for asynchronous
xmlHttpReq.send(null);
}
Today this is considered deprecated, because an async fetch call (in browsers later than 2016) is simpler and more robust.
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.