Nocturnal Practitioners of Magic


    2.6.1 • Public • Published


    An set of async/await utilities:

    • Eliminate try/catch in favor of error values
    • Create a promise handle to imperatively resolve and reject a promise
      • Useful for returning a single instance of a promise

    Also see array destructuring with default values for handling returned arrays.

    Change Log


    Require an Object With All Functions

    const catchify = require('catchify');

    Require Functions Individually

    const all = require('catchify/all');


    Resolve Promise to [error, value]

    const catchify = require('catchify');
    async function example(promise) {
      const [error, value] = await catchify(promise);
      if (error) console.log(error);

    Array Destructuring with a Default Value

    const catchify = require('catchify');
    async function example(promise) {
      const [error, value={message:'Hello'}] 
        = await catchify(promise);
      if (error) console.log(error);
      return value;

    Wait for all promises to resolve, regardless of error

    const some = require('catchify/some');
    async function example() {
      const [ [error1, error2], [value1, value2] ] = await some([
      if (error2) console.error('error2');
      if (value1) console.log('value1');

    Use a promise handle to return a single promise instance

    const catchify = require('catchify');
    let pending = null;
    async function example() {
      if (pending) return pending;
      const handle = catchify.newPromiseHandle();
      pending = handle.promise;
      const [error, value] = await catchify.resolve('example');
      pending = null;
      if (error) return handle.reject('rejected');
      return handle.resolve('resolved');



    • Equivalent to Promise.resolve(value)
    • catchify(value) is an alias for catchify.resolve(value)
    • Returns: [error, value]
    const [error, value] 
      = await catchify(promise)


    • Equivalent to Promise.resolve(value)
    • catchify.resolve(value) is an alias for catchify(value)
    • Returns: [error, value]
    const [error, value] 
      = await catchify.resolve('Quickly test the success path')


    const [error, value] 
      = await catchify.reject('Quickly test the error path')


    const [error, value] 
      = await catchify.race([promise1, promise2])


    • Similar to Promise.all(iterable) with the following differences:
      • Accepts either an object or an iterable
      • If there is an error, values will be an empty array||object so it is safe to use array||object destructuring
    • Returns: [error, values]
    const [error, [value1, value2]] 
      = await catchify.all([promise1, promise2])
    const [error, {a: value1, b: value2}]
      = await catchify.all({a: promise1, b: promise2})


    • Like catchify.all(iterable||object) but an error does not prevent resolution of the rest
    • Within errors, an error will be null if there was no error
    • Within values, the value will be null if there was an error
    • Returns: [errors, values]
    const [[error1, error2], [value1, value2]] 
      = await catchify.some([promise1, promise2])
    const [{a: error1, b: error2}, {a: value1, b: value2}] 
      = await catchify.some({a: promise1, b: promise2})

    catchify.limit(iterable||object, limit=2, exitOnError=false)

    • Like catchify.some(iterable||object) but it allows limiting concurrent asynchronous tasks
    • Promises have no way to delay start, so any function in iterable||object will be called on its turn
    • Values returned from called functions can be a Promise, which would provide the actual limiting functionality, or any other value for convenience, as it will be passed to Promise.resolve() before proceeding
    • If exitOnError=true, each subset is still executed like catchify.some(iterable) but execution will halt if there is an error
    • Returns: [errors, values]
    // The promises from fn1 and fn2 execute concurrently
    // fn3 is called after promises from fn1 and fn2 resolve
    const [
      [error1, error2, error3], 
      [value1, value2, value3]
    ] = await catchify.limit([fn1, fn2, fn3])
    const [
      {a: error1, b: error2, c: error3}, 
      {a: value1, b: value2, c: value3}
    ] = await catchify.limit({a: fn1, b: fn2, c: fn3})


    • Like new Promise((resolve, reject)=>{}) except you have a handle to call resolve and reject outside the function
    • The resolve and reject methods will return instances of the promise
    • The promise has NOT been wrapped with a call to catchify.resolve()
    • Returns {promise, resolve, reject}
    // Access the promise
    let pending;
    const handle = catchify.newPromiseHandle();
    pending = handle.promise;
    // Reject the promise
    const handle = catchify.newPromiseHandle();
    // Resolve the promise
    const handle = catchify.newPromiseHandle();




    npm i catchify

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