then-utils

A collection of useful, promise-returing utilities. No dependencies (other then Node builtins).

Utilities

All utilities return Promises.

callWithPromiseOrCallback

Arguments

• func - the function to call
• ...args - extra arguments to pass to the function

Description

Calls the given func with optional extra ...args, and a Node-style callback (error, data). If the function returns a Promise, then it attaches it's resolve and reject to that Promise. If the callback is called, then it will reject if error is given, or resolve with the given data.

Usage

const { callWithPromiseOrCallback } = require('then-utils');
const { addWithCallback, addWithPromise } = require('some-math-package');
 
callWithPromiseOrCallback(addWithCallback, 1, 2).then((result) => {
  console.log(result); // 3
}).catch((error) => {
  console.log('Oh no! Something blew up!');
  console.log(error.stack);
});
 
callWithPromiseOrCallback(addWithPromise, 3, 4).then((result) => {
  console.log(result); // 7
}).catch((error) => {
  console.log('What?! Math errors?');
  console.log(error.stack);
});

returnPromiseOrCallback

Arguments

• callbackArg - the callback argument
• handler - the Promise handler

Description

This function is mainly for API developers who still need to support callbacks but want to migrate to Promises. The callbackArg should be whatever your callback argument is in your function. If the callbackArg is a function, then it is called as a Node-style callback (error, data) when you resolve or reject in the handler. Otherwise, it returns a Promise with the given handler.

Usage

const { returnPromiseOrCallback } = require('then-utils');
 
function myAPI(someArgs, myOptionalCallback) {
  return returnPromiseOrCallback(myOptionalCallback, (resolve, reject) => {
    console.log('process some arguments:', someArgs);
    // process someArgs
    resolve();
  });
}
 
myAPI('Wow', (error) => {
  if (error) return console.error('Oh no!', error.stack);
  console.log('done processing it already? wow.');
});
 
myAPI('Cool').then(() => {
  console.log('done processing it already? ok then!');
}).catch((error) => {
  console.error('Aw man!', error.stack);
});

asyncFor

Arguments

• arrOrObjOrNum - an array, object, or number to loop on
• onloop - a function called for every iteration of the loop

Description

TL;DR, just see the usage below

Asynchronously loops using setImmediate. If arrOrObjOrNum is a number, it'll be converted into an array by pushing null into an array arrOrObjOrNum times, and looping on that. It uses Object.keys() to get the keys to loop through, except that if the key can be parsed to a Number (with parseInt()) then it'll convert it to a Number. It'll call onloop for every iteration of the loop with the current key (or index, for an array), the item at that position (null if arrOrObjOrNum is a number), and a breakLoop function (to exit the loop early). If onloop returns a Promise, it'll wait until the Promise is resolved to goto the next loop. If the Promise is rejected, it'll stop looping and reject it's own Promise. Otherwise, it'll add a Node-style callback (error, data) argument to onloop's arguments, where if given an error, it'll act as if it were rejected and end the loop.

Usage

const { asyncFor } = require('then-utils');
 
const myArray = [9, 3, 4];
const myObject = {
  nom: 'hi',
  foo: 8
};
 
asyncFor(myArray, (index, item) => {
  return new Promise((resolve, reject) => {
    console.log('index:', index);
    console.log('item:', item);
    resolve();
  });
}).then(() => {
  console.log('Wow, done!');
}).catch((err) => {
  console.error(err.stack);
});
 
asyncFor(4, (index, item) => {
  return new Promise((resolve, reject) => {
    console.log('index:', index);
    console.log('item:', item); // will always be null, since you passed a number, which means you just want to loop 4 times
    resolve();
  });
}); // then, catch handlers here...
 
asyncFor(myObject, (key, item) => {
  return new Promise((resolve, reject) => {
    console.log('key:', key);
    console.log('item:', item);
    resolve();
  });
}); // then, catch handlers here...
 
asyncFor(myArray, (index, item, breakLoop, cb) => {
  // you can also just use a callback instead of returning a Promise
  console.log('index:', index);
  console.log('item:', item);
  cb();
}); // then, catch handlers here...
 
asyncFor(myArray, (index, item, breakLoop) => {
  return new Promise((resolve, reject) => {
    if (index === 1) {
      return breakLoop(); // equivalent of `break`
    }
    // you must call `resolve` (or the callback) when you are done
    // it can also act as `continue` if you `return resolve()` before you're finished
    resolve();
  });
});

rmrf

Arguments

• pathname - the path to remove recursively (can be a folder or a file)

Description

Remove a file or folder from the specified pathname. If the path is a folder, it is removed recursively. If the file or folder isn't found, then it will resolve, since the goal (having the path not exist) is already achieved.

Usage

const { rmrf } = require('then-utils');
 
rmrf('some-path/i-wanna/delete').then(() => {
  console.log('great, done deleting the path');
}).catch((err) => {
  console.error('crap, something went wrong while deleting the path');
  console.error(err.stack);
});

mkdirp

Arguments

• pathname - the full path for the new folder

Description

Creates a folder at the specified path recursively, that is, it will create any folders that don't exist in the path.

Usage

const { mkdirp } = require('then-utils');
 
mkdirp('/i-exist/me-too/but-i-dont/me-neither/i-am-the-target-folder').then(() => {
  console.log('the whole path now exists, yeah!');
}).catch((err) => {
  conosle.error('oh man...');
  console.error(err.stack);
});

filterByExtension

Arguments

• pathname - the path search in to filter it's files
• ext - the extension to filter for

Description

Reads the files of the pathname, and filters them. If their extension matches the specified ext, then they will be returned.

Usage

const { filterByExtension } = require('then-utils');
 
filterByExtension('/path/i-want/to/search', '.js').then((files) => {
  console.log('now i have a list of all the files ending with \'.js\':');
  console.dir(files);
}).catch((err) => {
  console.error('what happened?');
  console.error(err.stack);
});

writeFile

Arguments

See fs.writeFile.

Description

Promise-ified fs.writeFile.

Usage

const { writeFile } = require('then-utils');
 
writeFile('/my/file/path', 'some file contents').then(() => {
  console.log('done writing file');
}).catch((err) => {
  console.error('crap');
  console.error(err.stack);
});

exec

Arguments

See child_process.exec.

Description

Promise-ified child_process.exec.

Usage

const { exec } = require('then-utils');
 
exec('ls $HOME', {
  env: {
    HOME: '/home/my-place'
  }
}).then(({ stdout, stderr }) => {
  console.log('done executing command');
  console.log(stdout);
  console.log(stderr);
}).catch((err) => {
  console.error('why?!');
  console.error(err.stack);
});

mv

Arguments

See fs.rename.

Description

Promise-ified fs.rename.

Usage

const { mv } = require('then-utils');
 
mv('/my/old/path', '/my/new/place').then(() => {
  console.log('done moving path');
}).catch((err) => {
  console.error('go away errors, i don\'t like you');
  console.error(err.stack);
});

cpr

Arguments

• frompath - the path to copy from
• topath - the path to copy to

Description

Copies a folder or file recursively from frompath to topath.

Usage

const { cpr } = require('then-utils');
 
cpr('/some/folder', '/put/me/here').then(() => {
  console.log('done copying folder');
}).catch((err) => {
  console.error('ugh errors');
  console.error(err.stack);
});

parseArgs

Arguments

• args - the arguments to parse

Description

Parses the given arguments into an object. I'm not going to spend time explaining this, just take the example.

Usage

const { parseArgs } = require('then-utils');
 
parseArgs(process.argv.slice(2)).then((args) => {
  // let's say process.argv.slice(2) === ['--hi', '--foo', '8', '-u']
  // then `args` would contain:
  args.hi === true;
  args.foo === '8';
  args.u === true;
}).catch((err) => {
  console.error('nope, i\'m not even gonna log this one');
});

spawn

Arguments

See child_process.spawn.

Description

Promise-ified child_process.spawn.

Usage

const { spawn } = require('then-utils');
 
const child = spawn('ls', ['$HOME'], {
  env: {
    HOME: '/home/my-place'
  }
});
 
child.cmd; // contains the spawned ChildProcess
 
child.then(() => {
  console.log('done executing this other command');
}).catch((err) => {
  console.error('well, i can\'t do anything about errors');
  console.error(err.stack);
});

sleep

Arguments

• ms - number of milliseconds to wait

Description

A "sleep" function (a.k.a. setTimeout), resolves after the given time is up.

Usage

const { sleep } = require('then-utils');
 
sleep(800).then(() => {
  console.log('800 milliseconds are up');
});

readFile

Arguments

See fs.readFile.

Description

Promise-ified fs.readFile.

Usage

const { readFile } = require('then-utils');
 
readFile('/my/file/path/to/read').then((cont) => {
  console.log('done reading file');
  console.log('file buffer:', cont);
}).catch((err) => {
  console.error('no, i... *sigh*');
  console.error(err.stack);
});