React Native中的意外承诺

Question

I am new to React Native and coding in general. I paid for some code on upwork and am having a hard time integrating it in my program.

async pullBatch(since){
    let param = {
        userScreenName: '?screen_name=google',
        count: "&count=5",
        retweets: "&include_rts=false",
        replies: "&exclude_replies=false",
        trim: "&trim_user=true",
        since: "&max_id=" + since
    };

    let twitterRest = new TwitterRest(); //create a new instance of TwitterRest Class   
    let batch = await twitterRest.pullTweets(param); //pull the Google TimeLine
    return batch;
}

pullTimeline(){
    let timeLine = []
    for(i = 0; i <= 2; i++){
        let currentBatch = this.pullBatch("1098740934588751900")
        console.log(currentBatch);
        timeLine = timeLine.concat(currentBatch);
    }
    console.log(timeLine);
    // timeLine = currentBatch
    return(timeLine)
}

I believe that when running pullTimeLine() the program is returning an array of three promises. (I have also run the code with "await" before pullBatch(), but it is erroring out telling me await is a reserved word) This means I am making two mistakes:

1. I am not correctly understanding promises in JS or how they are resolved.
2. I am incorrectly concatenating the arrays.

I am constantly trying to learn, so while I greatly appreciate suggestions for code fixes, I also really would appreciate if you'd teach me about where my lapses in understanding lies.

Thank you

Answer 1

Let's break it down. You seem to understand that pullBatch is an async function, and so calling it will return a promise create by the twitterRest interaction.

The problem is that your call to pullBatch inside your for loop will not resolve these promise (which seems to be what you want to do). The easiest way is to use await for currentBatch , but as you tried, you got the reserved error. Basically you just need to also make pullTimeline async like this:

async pullTimeline(){
  ...

Just realise that once you do this, pullTimeline is now an async function that will also return a promise. So to use this function you need to either use .then() , for example:

pullTimeline().then(timeLine => {
  // do something with your timeline here
})

Or if you are using it within another async function, you can use await.

const timeLine = await pullTimeline() // must be inside async function

Basically at some point in your calling chain, you will have to resolve a promise using .then() , or disregard the top level promise by making a top level async function. For example:

async useTimeline() {
  const timeLine = await pullTimeline()
  // do something with your timeline
}

// call the function above, and just disregard its promise
useTimeLine()

Just don't forget to handle errors somewhere. Either use a .catch() on your top level promise, or use try / catch around any of your await calls.