Expected to return a value at the end of arrow function
39 e.preventDefault();
40 search.addEventListener("change", (e) => {
41 userInput = String(e.target.value).toLowerCase().trim();
42 let FilteredTimeZoneArray = allTimezonesArray.filter((eachTimeZone) => {43 let eachTimeZoneString = String(eachTimeZone.textContent).toLowerCase();
44 if (eachTimeZoneString.includes(userInput)) {
45 eachTimeZone.parentElement.style.display = "block";
Description
Any code paths that do not have explicit returns will return undefined.
It is recommended to replace any implicit dead-ends that return undefined with a return null statement.
As a convention, undefined signals that an unexpected value has been produced as the
result of a logical error in the program.
A null return, on the other hand, signals that the input to a function was incorrect,
or a value was 'not found'.
Having this distinction in code helps you figure out if something was caused because of a logical error, or malformed input to a function call.
Bad Practice
function getUser(name) {
if (userExists(name)) {
return userDb.get(name);
}
// whoops! Implicit undefined return
}
function readFile(fileName) {
if (fs.existsSync(fileName)) {
return fs.readFileSync(fileName, 'utf-8');
}
return; // Implicit undefined return.
}
Recommended
function getUser(name) {
if (userExists(name)) {
return userDb.get(name);
}
// `null` indicates there is no such user.
return null;
}
function readFile(fileName) {
if (fs.existsSync(fileName)) {
return fs.readFileSync(fileName, 'utf-8');
}
// `null` indicates there is no such file.
return null;
}