try-catch-core

Low-level package to handle completion and errors of sync or asynchronous functions, using once and dezalgo libs. Useful for and used in higher-level libs such as always-done to handle completion of anything.

Table of Contents

• Install
• Usage
• Background
  • What is this?
  • Why this exists?
  • What is useful for?
  • Why not plain try/catch?
• API
  • tryCatchCore
• Supports
  • Successful completion of sync functions
  • Failing completion of synchronous
  • Completion of async functions (callbacks)
  • Failing completion of callbacks
  • Passing custom context
  • Passing custom arguments
  • Returning a thunk
• Related
• Contributing

Install

npm i try-catch-core --save

Usage

For more use-cases see the tests

const fs = require('fs')
const tryCatchCore = require('try-catch-core')

tryCatchCore((cb) => {
  fs.readFile('./package.json', 'utf8', cb)
}, (err, res) => {
  if (err) return console.error(err)

  let json = JSON.parse(res)
  console.log(json.name) // => 'try-catch-core'
})

Background

Why this exists? What is useful for? What's its core purpose and why not to use something other? Why not plain try/catch block? What is this?

What is this?

Simply said, just try/catch block. But on steroids. Simple try/catch block with a callback to be called when some function completes - no matter that function is asynchronous or synchronous, no matter it throws.

Why this exists?

There are few reasons why this is built.

• simplicity: built on try-catch-callback, once and dezalgo - with few lines of code
• flexibility: allows to pass custom function context and custom arguments
• guarantees: completion is always handled and always in next tick
• low-level: allows to build more robust wrappers around it in higher level, such as always-done to handle completion of anything - observables, promises, streams, synchronous and async/await functions.

What is useful for?

It's always useful to have low-level libs as this one. Because you can build more higher level libs on top of this one. For example you can create one library to handle completion of generator functions. It would be simply one type check, converting that generator function to function that returns a promise, than handle that promise in the callback.

Brilliant example of higher level lib is always-done which just pass given function to this lib, and handles the returned value inside callback with a few checks.

Another thing can be to be used as "thunkify" lib, because if you does not give a callback it returns a function (thunk) that accepts a callback.

Why not plain try/catch?

Guarantees. This package gives you guarantees that you will get correct result and/or error of execution of some function. And removes the boilerplate stuff. Also works with both synchronous and asynchronous functions. But the very main thing that it does is that it calls the given callback in the next tick of event loop and that callback always will be called only once.

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API

tryCatchCore

Executes given fn and pass results/errors to the callback if given, otherwise returns a thunk. In below example you will see how passing custom arguments can be useful and why such options exists.

Params

• <fn> {Function}: function to be called.
• [opts] {Object}: optional options, such as context and args, passed to try-catch-callback
• [opts.context] {Object}: context to be passed to fn
• [opts.args] {Array}: custom argument(s) to be pass to fn, given value is arrayified
• [opts.passCallback] {Boolean}: pass true if you want cb to be passed to fn args.
• [cb] {Function}: callback with cb(err, res) signature.
• returns {Function} thunk: if cb not given.

Example

var tryCatch = require('try-catch-core')
var options = {
  context: { num: 123, bool: true }
  args: [require('assert')]
}

// `next` is always there, until
// you pass `passCallback: false` to options
tryCatch(function (assert, next) {
  assert.strictEqual(this.num, 123)
  assert.strictEqual(this.bool, true)
  next()
}, function (err) {
  console.log('done', err)
})

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Supports

Handle completion of synchronous functions (functions that retunrs something) and asynchronous (also known as callbacks), but not async/await or other functions that returns promises, streams and etc - for such thing use always-done.

Successful completion of sync functions

const tryCatchCore = require('try-catch-core')

tryCatchCore(() => {
  return 123
}, (err, res) => {
  console.log(err, res) // => null, 123
})

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Failing completion of synchronous

const tryCatchCore = require('try-catch-core')

tryCatchCore(() => {
  foo // ReferenceError
  return 123
}, (err) => {
  console.log(err) // => ReferenceError: foo is not defined
})

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Completion of async functions (callbacks)

const fs = require('fs')
const tryCatchCore = require('try-catch-core')

tryCatchCore((cb) => {
  // do some async stuff
  fs.readFile('./package.json', 'utf8', cb)
}, (e, res) => {
  console.log(res) // => contents of package.json
})

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Failing completion of callbacks

const fs = require('fs')
const tryCatchCore = require('try-catch-core')

tryCatchCore((cb) => {
  fs.stat('foo-bar-baz', cb)
}, (err) => {
  console.log(err) // => ENOENT Error, file not found
})

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Passing custom context

const tryCatchCore = require('try-catch-core')
const opts = {
  context: { foo: 'bar' }
}

tryCatchCore(function () {
  console.log(this.foo) // => 'bar'
}, opts, () => {
  console.log('done')
})

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Passing custom arguments

It may be strange, but this allows you to pass more arguments to that first function and the last argument always will be "callback" until fn is async or sync but with passCallback: true option.

const tryCatchCore = require('try-catch-core')
const options = {
  args: [1, 2]
}

tryCatchCore((a, b) => {
  console.log(arguments.length) // => 2
  console.log(a) // => 1
  console.log(b) // => 2

  return a + b + 3
}, options, (e, res) => {
  console.log(res) // => 9
})

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Returning a thunk

Can be used as thunkify lib without problems, just don't pass a done callback.

const fs = require('fs')
const tryCatchCore = require('try-catch-core')
const readFileThunk = tryCatchCore((cb) => {
  fs.readFile('./package.json', cb)
})

readFileThunk((err, res) => {
  console.log(err, res) // => null, Buffer
})

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Related

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Contributing

Pull requests and stars are always welcome. For bugs and feature requests, please create an issue.
But before doing anything, please read the CONTRIBUTING.md guidelines.

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