Local variable name shadows variable in outer scope JS-0123
Bug risk
Minor
a year ago
—
2 years old
'err' is already declared in the upper scope on line 152 column 84
177
178 try {
179 response.send(str)
180 } catch(err) {181 console.error(err)
182 }
183 })'err' is already declared in the upper scope on line 47 column 54
49 process.stderr.write(tolog); //just write it to stderr
50 }
51 else {
52 appendFile(__dirname + "/logs/" + time, tolog, function (err) { 53 if (err) {
54 process.stderr.write(err);
55 }'ws' is already declared in the upper scope on line 10 column 13
425 threshold: 1024 * 16
426 }
427});
428wss.on("connection", function connection(ws) {429 ws.channel = "everyone";
430 console.log(5,"new connection");
431 ws.on("message", function incoming(message) {'err' is already declared in the upper scope on line 22 column 41
41 }).toBuffer().then(function(data){
42 writeFileSync(avatars + filename,data)
43 let sql = `update ipost.users set User_Avatar=? where User_Name=?`;
44 con.query(sql, [filename, encodeURIComponent(res.locals.username)], function (err) { 45 if (err)
46 throw err;
47 res.json({ "success": "updated avatar" });'values' is already declared in the upper scope on line 143 column 13
146 throw err;
147 if (result[0]) {
148 let sql = `update ipost.users set User_PW=? where User_Name=? and User_PW=?;`;
149 let values = [hashed_new_pw, res.locals.username, hashed_pw];150 con.query(sql, values, (err2) => {
151 if (err2)
152 throw err2;
Description
Two variables can have the same name if they're declared in different scopes.
In the example below, the parameter x is said to "shadow" the variable x declared above it.
The outer x can no longer be accessed inside the sum function.
const x = 1
function add(x, y) {
return x + y
}
While shadowing does not cause any problems most of the time, it does make the code harder to read and understand. We highly recommend against shadowing. However, if you want to shadow some variable name and don't want DeepSource to flag it, add a skipcq comment alongside an explanation:
const x = 1
function add(x, y) { // skipcq: JS-0123 - `x` can be safely shadowed
return x + y
}
If you want to disable this issue project-wide, you can add it to the list of disabled issues in the project dashboard.
Bad Practice
const file = "data.txt"
function readFile(file) {
// The parameter `file` shadows the toplevel variable `file`.
if (fs.existsSync(file)) {
return fs.readFileSync(file)
}
return null
}
Recommended
// Prefer variable names that are distinct and convey as much
// meaning as possible.
const dataFile = "data.txt"
function readFile(filePath) {
if (fs.existsSync(filePath)) {
return fs.readFileSync(filePath)
}
return null
}
Alternatively:
const file = "data.txt"
function readFile(file) { // skipcq: JS-0123 - Shadowing is safe here
// ...
}