How to execute shell commands synchronously in Node?

Question

I'm trying to execute some shell commands synchronously to install npm dependencies, build packages and create a database in docker.

    ['api', 'front-end'].forEach(async (dir) => {
        await new Promise((resolve, reject) => {
          console.log(`Installing npm dependencies for ${dir}`);
          exec('npm install', { cwd: path.join(initDir, 'pushkin', dir) }, (err) => {
            if (err) console.error(`Failed to install npm dependencies for ${dir}: ${err}`);
            if (dir !== 'api' && dir !== 'front-end') return;
          });
          resolve(`${dir} installed...`);
        })
          .then(() => {
            console.log(`Building ${dir}`);
            exec('npm run build', { cwd: path.join(process.cwd(), 'pushkin', dir) }, (err) => {
              if (err) console.error(`Failed to build ${dir}: ${err}`);
              console.log(`${dir} is built`);
            });
          })
          .then(() => {
            shell.exec(startDbCommand);
          })
          .then(() => {
            shell.exec(createDbCommand);
          })
          .then(() => {
            shell.exec(stopDbCommand);
          });
      });

The docker commands are:

const startDbCommand = 'docker-compose -f pushkin/docker-compose.dev.yml up --no-start && docker-compose -f pushkin/docker-compose.dev.yml start test_db';
const createDbCommand = 'docker-compose -f pushkin/docker-compose.dev.yml exec -T test_db psql -U postgres -c "create database test_db"';
const stopDbCommand = 'docker-compose -f pushkin/docker-compose.dev.yml stop test_db';

When I ran it for the first time, I got this error:

No container found for test_db_1

Failed to build front-end: Error: Command failed: npm run build
sh: react-scripts: command not found

Failed to build api: Error: Command failed: npm run build
sh: babel: command not found

However, after I ran it again for the second time, everything seems to be fine. Is this a problem about the Promise chain I wrote? Thanks.

synchronously? Your questions is slightly mixed up, your using promises, did you mean asynchronously.. If you wanted synchronously you would use execSync — Keith
– Keith, Commented May 5, 2020 at 9:05
Promises don't make anything synchronous. They can help making asynchronous things sequential though — Bergi
– Bergi, Commented May 5, 2020 at 9:10
I have no idea why would you do this in nodejs? Why not run everything in dockerfile / docker-compose file? — Shnigi
– Shnigi, Commented May 5, 2020 at 9:23

Matt · Accepted Answer · 2020-05-05 10:33:29Z

Two important things are the running commands in order one after the other (I believe that's what you mean by synchronously?) and also bailing when there is a failure.

The project directory loop also looks out of place. At the moment it loops over everything, including the db setup commands. It looks like you are doing test setup, so I believe the "synchronous" order is:

npm install/build for api
npm install/build for frontend
database setup

So first, create a promise out of nodes spawn so you can await it.

function runProcessToCompletion(cmd_array, options){
  return new Promise((resolve, reject) => {

    const result = {
      cmd: cmd_array,
      options,
      code: null,
      output: [],
    }

    const proc = spawn(cmd_array[0], cmd_array.slice(1), options)

    proc.on('error', (error) => {
      error.result = result
      reject(error)
    })

    proc.on('close', code => {
      result.code = code
      if (code !== 0) {
        const error = new Error(`PID "${proc.pid}" exited with code "${code}"`)
        error.result = result
        reject(error)
      }
      console.log(`Spawned PID "${proc.pid}" exited with code "${code}"`)
      resolve(result)
    })

    proc.stdout.on('data', (data) => {
      result.output.push(data.toString())
      process.stdout.write(data)
    })

    proc.stderr.on('data', (data) => {
      result.output.push(data.toString())
      process.stderr.write(data)
    })

    if (proc.pid) {
      console.log(`Spawned PID "${proc.pid}" for "${cmd_array.join(' ')}"`)
    }
  })
}

Then you can more easily structure your code as a simple list of commands. The benefit of using spawn is you can avoid all the shell-isms. The downside is you miss out on all the shell-isms.

For example the paths to executables need to be fully defined without a shells PATH

const path = require('path')
const initDir = process.cwd()
const project_dirs = ['api', 'front-end']
const setupDbCommand = ['/usr/local/bin/docker-compose','-f','pushkin/docker-compose.dev.yml','up','--no-start']
const startDbCommand = ['/usr/local/bin/docker-compose','-f','pushkin/docker-compose.dev.yml','start','test_db']
const createDbCommand = ['/usr/local/bin/docker-compose','-f','pushkin/docker-compose.dev.yml','exec','-T','test_db','psql -U postgres -c "create database test_db"']
const stopDbCommand = ['/usr/local/bin/docker-compose','-f','pushkin/docker-compose.dev.yml','stop','test_db']

async function go(){
  for (let dir of project_dirs) {
    const cwd = path.join(initDir, 'pushkin', dir)
    await runProcessToCompletion(['/usr/local/bin/npm','install'], { cwd })
    await runProcessToCompletion(['/usr/local/bin/npm','run','build'], { cwd })
  }
  await runProcessToCompletion(setupDbCommand)
  await runProcessToCompletion(startDbCommand)
  await runProcessToCompletion(createDbCommand)
  await runProcessToCompletion(stopDbCommand)
  return true
}

go().catch(err => {
  console.error(err)
  console.error(err.results)
})

If it's too hard without the shell stuff, you can turn that back on with the spawn options

{ shell: true }

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