Go-promise

This is an experimental implementation of javascript's promise in golang. Why implement this? Actually, golang is not suitable to implement generic purpose library and it has a good async funtion with select, go routine, channel. I have to say those tools are powerful. In javascript, you have to use promise or async await to achieve the same effect. However, I think promise is a asynchronous pattern not a basic async funtion so I am interested at implementation it in golang. That's why I create this repo.

How to install

go get -u github.com/sillygod/go-promise

Example Usages

a simple example list in the following. Note I ignore the package name (promise)

p := New(func(resolve func(interface{}), reject func(error)) {
    resolve("sonla")
})

p.Then(func(data interface{}) interface{} {
    t.Logf("What I get is %v\n", data.(string))
    assertEqual(t, "sonla", data.(string))
    return nil
})

Await(p)

or more simple usage

p := Resolve("hello")
value := Await(p)

I change the behavior of promise.then in my implementation because golang doesn't support optional arguement. If we want the function then to accept onSuccess and onError, we need to define function signature of then to accept both function. We can not ignore one of them when we call it. For example,

var p = new Promise((resolve, reject) => {
   resolve("hi")
}).then((value) => {
   console.log(value)
})

// in js we can only accept onSuccess but in golang..
// it will be like the following
// p.Then(func(data interface{}), interface{}, func(err error){
// })

I feel uncomfortable with that so I change the behavior a little :p

The following shows the chain feature of promise in javascript

example code from here

new Promise((resolve, reject) => {
    console.log('Initial');

    resolve();
})
.then(() => {
    throw new Error('Something failed');
        
    console.log('Do this');
})
.catch(() => {
    console.log('Do that');
})
.then(() => {
    console.log('Do this, no matter what happened before');
});

In my library, will look like the following

p := New(func(resolve func(interface{}), reject func(error)) {
    fmt.Println("Initial")
    resolve("Initial")
})

p.Then(func(data interface{}) interface{} {
    panic("Something failed")

    fmt.Println("Do this")
    return nil
}).Catch(func(err error) {
    fmt.Println("Do that")
}).Then(func(data interface{}) interface{} {
    fmt.Println("Do this, no matter what happened before")
    return nil
})

Await(p)

I also implement all and race feature and you can see them in the test file.