Git hook written on JavaScript

Question

As in many teams, me and my coworkers are putting ticket number into beginning of each commit message. If your branches are starting with ticket number it is easy to create prepare-commit-msg hook to automate this action, and since I'm a front-end deveoper, I decided to write it as a nodejs script. Look at what I came up with and tell me how to make it better if you will.

#.git/hooks/prepare-commit-msg

#!/usr/bin/env node

const fs = require('fs')
const { exec } = require('child_process')

const COMMIT_EDITMSG = process.argv[2]

exec('git symbolic-ref --short HEAD', (err, stdout) => {
    if (err) throw err

    fs.readFile(
        COMMIT_EDITMSG,
        'utf8',
        (err, message) => {
            if (err) throw err

            fs.writeFile(
                COMMIT_EDITMSG,
                `${stdout.replace(/(-|_).*/, '')} ${message}`.replace(/\n/, ''),
                err => {
                    if (err) throw err
                }
            )
        }
    )
})

You most definitely want to be using return console.error(...) in all those error scenarios :) — James
– James, Commented Jun 28, 2018 at 0:09
Would you advise to throw an error instead of loging it trough console.error? — askhat
– askhat, Commented Jun 28, 2018 at 9:19
even better! Point is, something bad has happened that shouldn't have, you don't want to let the hook continue, with your current code it would. — James
– James, Commented Jun 28, 2018 at 9:46

James · Accepted Answer · 2018-06-28 11:24:27Z

1

Outwith the improved error handling as per the comments, another improvement on this be to write the hook using a more synchronous approach e.g.

#.git/hooks/prepare-commit-msg
#!/usr/bin/env node

const { readFileSync, writeFileSync } = require('fs')
const { execSync } = require('child_process')
const COMMIT_EDITMSG = process.argv[2];

const stdout = execSync('git symbolic-ref --short HEAD');
const message = readFileSync(COMMIT_EDITMSG, 'utf-8');
writeFileSync(COMMIT_EDITMSG, `${stdout.replace(/(-|_).*/, '')} ${message}`.replace(/\n/, ''));

This completely eliminates the need for callbacks and, naturally, if an error occurs the commit should be blocked - it's also a lot more succinct and easier to read.

edited Jun 28, 2018 at 11:24

answered Jun 28, 2018 at 10:55

James

5672 silver badges8 bronze badges

\$\begingroup\$ Thank you, to my shame I wasn't been aware of syncronous versions of this functions \$\endgroup\$

askhat
– askhat

2018-06-28 11:13:54 +00:00
Commented Jun 28, 2018 at 11:13
\$\begingroup\$ @askhat whoops, that's a mistake, it should be using that! Updated. \$\endgroup\$

James
– James

2018-06-28 11:24:11 +00:00
Commented Jun 28, 2018 at 11:24

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