logical-promise

Logical operators on Promises


Keywords
logical-promise, template-literals, promise, ternary operators, logical operators, nodejs
License
MIT
Install
npm install logical-promise@1.0.2

Documentation

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logical-promise

logical-promise uses template literals to perform logical operators on Promises.

logical-promise will change the way you write Promises.

Supported operators:

  • Logical AND: &&
  • Logical OR: ||
  • Logical NOT: !
  • Parenthese: ( and )
  • Conditional(ternary) operators: ? and :

Install

$ npm install logical-promise

Examples

import logical, {
  FULLFILLED,
  FULLFILLED_AND_TRUE
} from 'logical-promise'

const resolve = n => Promise.resolve(n)
const reject = n => Promise.reject(n)

1. By default, if rejected, then go into logical OR

logical `${reject(1)} || ${resolve(0)}`
// Promise.resolve(0)

2. Specify condition method. Equivalent to example 1.

logical(FULLFILLED) `${reject(1)} || ${resolve(0)}`
// Promise.resolve(0)

3. Change the behavior using condition method

logical `
  ${reject(1)}
  || ${resolve(0)}
  || ${resolve(2)}
`
// Promise.resolve(0)

logical(FULLFILLED_AND_TRUE) `
  ${reject(1)}
  || ${resolve(0)}
  || ${reject(2)}
`
// Promise.reject(2)

4. Uses factory functions that return promises.

import {
  factory
} from 'logical-promise'

factory `
  ${() => Promise.reject(1)}
  && ${() => Promise.resolve(0)}
`
// Promise.reject(1)

By using factory, we could prevent unnecessary Promise branch from executing. For example:

import delay from 'delay'

let obj
const p1 = () => delay(10).then(() => {
  obj = {a: 1}
})
const p2 = () => obj.a
logical `${p1()} && ${p2()}`   // Booooooooooooom !!!

If use factory:

obj = null

factory `${p1} && ${p2}`       // Promise.resolve(1)

5. You could also use condition method with factory

factory(FULLFILLED_AND_TRUE) `
  ${() => reject(1)}
  || ${() => resolve(0)}
  || ${() => resolve(2)}
`
// Promise.resolve(2)

6. Ternary operators (a ? b : c) are also supported

const f = n => resolve(n)

factory(FULLFILLED_AND_TRUE) `
  ${f(0)}
    ? ${f(1)}
    // We can also write comments here.
    // Even nested ternary operators are supported.
    : ${f(0)}
      ? ${f(2)}
      : ${f(3)} && ${f(4)}
`
// Promise.resolve(4)

7. Promises are not always required, but it always returns a Promise

logical(FULLFILLED_AND_TRUE) `${0} || ${resolve(1)}`
// Promise.resolve(1)

factory(FULLFILLED_AND_TRUE) `${() => 0} || ${() => 1}`
// Promise.resolve(1)

Usage

logical(operators, ...promises)

logical `template`
logical(condition) `template`
factory `template`
factory(condition) `template`
  • condition function(promise: Promise): Boolean The method to check whether a expression should be treated as true.

Returns Promise

Built-in condition methods.

FULLFILLED

const FULLFILLED = promise => promise.then(
  () => true,
  () => false
)

FULLFILLED_AND_TRUE

const FULLFILLED_AND_TRUE = promise => promise.then(
  result => !!result,
  () => false
)

How does it work

If you have figured it out how template literals works, then it is easy to find out that the example 1 is equivalent to:

// Spaces will be trimmed
logical(['', ' || ', ''], reject(1), resolve(0))

Template literals do a great job to tokenize the source code for us 😆 ~

License

MIT