tslint Error - Shadowed name: 'err'

Question

tslint is currently throwing the following error

Shadowed name: 'err'

Here is the code

fs.readdir(fileUrl, (err, files) => {
        fs.readFile(path.join(fileUrl, files[0]), function (err, data) {
            if (!err) {
                res.send(data);
            }
        });
    });

Anybody have a clue on what the best way would be to solve this and what the error even means?

Answer 1

You are using the same variable "err" in both outer and inner callbacks, which is prevented by tslint.

If you want to use the same variable then "no-shadowed-variable": false, otherwise do as below.

fs.readdir(fileUrl, (readDirError, files) => {
    fs.readFile(path.join(fileUrl, files[0]), function (err, data) {
            if (!err) {
                res.send(data);
            }
        });
    });

Answer 2

Add this comment just above the error line--

// tslint:disable-next-line:no-shadowed-variable

Answer 3

This shadowed name tslint error is due to repetition of the name 'err' twice in your callback functions. You can change either anyone 'err' to other name so this should work.

Example: This should work

fs.readdir(fileUrl, (error, files) => {
        fs.readFile(path.join(fileUrl, files[0]), function (err, data) {
            if (!err) {
                res.send(data);
            }
        });
    });

Answer 4

When same variable is declared multiple times in same scope, this warning occurs.

Use different variable names in such cases.