47 { ...options }
48 ));
49 ob.observe(element);
50 return () => {51 cleanOb();52 };53 }, [element, options]);
54
55 // return { isIntersecting };
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.
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.
}
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;
}