Using async/await not working

Question

I have a function and it does async db search operation.

var get_all_channels = function {
    return new Promise(()=> {
        db.find({type:'pricing'},{channel_name:1},function(err,docs){
        if(err)
            return err;
        var c = []
        docs.forEachOf(function(ch){
            c.push(ch['channel_name'])
        })
        return c;
    })
    })
}

async function send(){
    return await get_all_channels()
}
function calculate(){
    send().then(res => alert(res))    
}

Here, the above function is not working. I don't know why? Please help me fix this function.

Alberto Trindade Tavares · Accepted Answer · 2017-07-20 07:22:05Z

2

You need to resolve the promise with the results, the array c, in get_all_channels:

var get_all_channels = function {
    return new Promise((resolve, reject)=> {
        db.find({type:'pricing'},{channel_name:1},function(err,docs){
        if(err) {
            reject(err)
            return
        }

        var c = []
        docs.forEachOf(function(ch){
            c.push(ch['channel_name'])
        })

        resolve(c)
    })
    })
}

And in calculate, you can also use await if you want, and, as pointed by @netchkin, you don't need the async/await in send as long as it just returns the await:

function send(){
   return get_all_channels()
}

async function calculate(){
   alert(await send())  
}

edited Jul 20, 2017 at 7:22

answered Jul 20, 2017 at 7:12

Alberto Trindade Tavares

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8 Comments

Alberto Trindade Tavares Over a year ago

When you create a promise, you need to pass two callbacks, a resolve and a reject. You need to call the resolve with the results when everything is ok, and call reject with the error when it goes wrong

netchkin Over a year ago

if your async function only returns await, you don't need async await at all. Just pass through the promise. async function send(){ return await get_all_channels() } becomes function send(){ return get_all_channels() }, which can be deleted

bigbounty Over a year ago

So,how do you do that? This promise thing is very confusing for me @netchkin

netchkin Over a year ago

@bigbounty I have modified my comment, if you have any questions regarding promises, feel free to ask them :)

netchkin Over a year ago

@bigbounty: you can use directly get_all_channels function whereever you need. You just need to take into account the call context - if you call get_all_channels from an async function, you should do const channels = await get_all_channels(). If you call it from a sync function, then you need to use .then() or catch() to react on the result of get_all_channels

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