Run another yarn/npm task within a package.json, without specifying yarn or npm

One simple approach is to use the npm-run-all package, whose documentation states:

Yarn Compatibility

If a script is invoked with Yarn, npm-run-all will correctly use Yarn to execute the plan's child scripts.

So you can do this:

"predeploy": "run-s build",
"deploy": "./deploy.sh",

And the predeploy step will use either npm or yarn depending on how you invoked the deploy task.

I think it is good to have the runs in package.json remain package manager agnostic so that they aren't tied to a specific package manager, but within a project, it is probably prudent to agree on the use of a single package manager so that you're not dealing with conflicting lockfiles.

It's probably not ideal, but you could run a .js file at your project root to make these checks...

You could create a file at your project root called yarnpm.js (or whatever), and call said file in your package.json deploy command..

// package.json (trimmed)
"scripts": {
  "deploy": "node yarnpm",
  "build": "whatever build command you use"
},

// yarnpm.js
const fs = require('fs');

const FILE_NAME = process.argv[1].replace(/^.*[\\\/]/, '');

// Command you wish to run with `{{}}` in place of `npm` or `yarn'
// This would allow you to easily run multiple `npm`/`yarn` commands without much work
// For example, `{{}} run one && {{}} run two
const COMMAND_TO_RUN = '{{}} run build; ./deploy.sh';

try {
  if (fs.existsSync('./package-lock.json')) {  // Check for `npm`
    execute(COMMAND_TO_RUN.replace('{{}}', 'npm'));
  } else if (fs.existsSync('./yarn.lock')) {   // Check for `yarn`
    execute(COMMAND_TO_RUN.replace('{{}}', 'yarn'));
  } else {
    console.log('\x1b[33m', `[${FILE_NAME}] Unable to locate either npm or yarn!`, '\033[0m');
  }
} catch (err) {
  console.log('\x1b[31m', `[${FILE_NAME}] Unable to deploy!`, '\033[0m');
}

function execute(command) { // Helper function, to make running `exec` easier
  require('child_process').exec(command,
    (error, stdout, stderr) => {
      if (error) {
        console.log(`error: ${error.message}`);
        return;
      }
      if (stderr) {
        console.log(`stderr: ${stderr}`);
        return;
      }
      console.log(stdout);
    });
}

Hope this helps in some way! Cheers.

EDIT:

...or if you wanted to parameterize the yarnpm.js script, to make it easily reusable, and to keep all "commands" inside the package.json file, you could do something like this..

// package.json (trimmed, parameterized)
"scripts": {
    "deploy": "node yarnpm '{{}} run build; ./deploy.sh'",
    "build": "node build.js"
},

// yarnpm.js (parameterized)
const COMMAND_TO_RUN = process.argv[2]; // Technically, the first 'parameter' is the third index
const FILE_NAME = process.argv[1].replace(/^.*[\\\/]/, '');

if (COMMAND_TO_RUN) {
  const fs = require('fs');

  try {
    if (fs.existsSync('./package-lock.json')) {  // Check for `npm`
      execute(COMMAND_TO_RUN.replace('{{}}', 'npm'));
    } else if (fs.existsSync('./yarn.lock')) {   // Check for `yarn`
      execute(COMMAND_TO_RUN.replace('{{}}', 'yarn'));
    } else {
      console.log('\x1b[33m', `[${FILE_NAME}] Unable to locate either npm or yarn!`, '\033[0m');
    }
  } catch (err) {
    console.log('\x1b[31m', `[${FILE_NAME}] Unable to deploy!`, '\033[0m');
  }

  function execute(command) { // Helper function, to make running `exec` easier
    require('child_process').exec(command,
      (error, stdout, stderr) => {
        if (error) {
          console.log(`error: ${error.message}`);
          return;
        }
        if (stderr) {
          console.log(`stderr: ${stderr}`);
          return;
        }
        console.log(stdout);
      });
  }
} else {
  console.log('\x1b[31m', `[${FILE_NAME}] Requires a single argument!`, '\033[0m')
}

What if check before run?

You can create a new file called build.sh, and it's content below:

# check if current user installed node environment, if not, auto install it.
if command -v node >/dev/null 2>&1; then
    echo "version of node: $(node -v)"
    echo "version of npm: $(npm -v)"
else
    # auto install node environment, suppose platform is centos, 
    # need change this part to apply other platform.
    curl --silent --location https://rpm.nodesource.com/setup_12.x | sudo bash -
    yum -y install nodejs
fi

npm run build

Then your script will be:

{
  "deploy": "./build.sh && ./deploy.sh"
}

So I think I have a much simpler solution:

"deploy": "yarn run build || npm run build; ./deploy.sh",

Its only real downside is in the case where yarn exists, but the build fails, then npm run build will also take place.