why does my nodejs function returning undefined? - node.js

Question

function getUserByStudentId(NIM) {
db.query('SELECT * FROM data_admin WHERE id_mahasiswa = ?', [NIM], async (err, result) => {
if (!result) {
return null
} else {
var data = await {
id: result[0].id_Admin,
email: result[0].email,
jabatan: result[0].jabatan,
password: result[0].password,
id_mahasiswa: result[0].id_mahasiswa,
id_Acara: result[0].id_Acara,
id_Organisasi: result[0].id_Organisasi
}
console.log(data) // there is a value here
return data
}
})
}
console.log(getUserByStudentId('1301194051')) // undefined returned
I'm a student and start learning nodejs. Would you explain to me, why my function returning undefined
console.log(getUserByStudentId('1301194051')) // undefined
but when I console.log on the function I got returned value

Answer 1

I'll promisify the function for you:
function getUserByStudentId(NIM) {
return new Promise(function(resolve, reject) => {
db.query('SELECT * FROM data_admin WHERE id_mahasiswa = ?', [NIM], (err, result) => {
if (!result) {
resolve(null);
} else {
var data = {
id: result[0].id_Admin,
email: result[0].email,
jabatan: result[0].jabatan,
password: result[0].password,
id_mahasiswa: result[0].id_mahasiswa,
id_Acara: result[0].id_Acara,
id_Organisasi: result[0].id_Organisasi
}
console.log(data) // there is a value here
resolve(data);
}
});
});
}
If you're going to use this function in global scope, use then:
getUserByStudentId('1301194051').then(result => {
console.log(result);
});
If you want to use this function inside an async function, you can await the result:
async function doSomethingWithUser(NIM) {
const user = await getUserByStudentId(NIM);
}
For example, if you're using express:
app.get('/user/:id', async (res, req) => {
const NIM = req.param.id;
const user = await getUserByStudentId(NIM);
res.json({ user });
});