isPromise

101 bytes

Usage

The isPromise function checks if a value is “Promise-like” by determining if it has a then method.

import * as _ from 'radashi'

_.isPromise({ then: () => {} }) // => true
_.isPromise(new Promise(() => {})) // => true
_.isPromise(Promise.resolve(1)) // => true
_.isPromise(Promise.reject(new Error('nope'))) // => true

_.isPromise('hello') // => false
_.isPromise({}) // => false

This approach is useful for identifying objects that conform to the Promise interface without actually being instances of Promise. It’s particularly helpful in scenarios where:

1. You need to quickly check if a value is thenable without resolving it.
2. Performance is critical, and you want to avoid the overhead of Promise.resolve.
3. You’re working with custom Promise implementations or third-party libraries that use Promise-like objects.

While Promise.resolve is generally recommended for handling both Promise and non-Promise values uniformly, isPromise can be preferable when you need to make decisions based on whether a value is Promise-like without actually resolving or chaining it. This can be especially useful in type-checking scenarios or when implementing control flow that depends on whether a value is immediately available or needs to be awaited.