Promises Loop

Question

So I followed the course material and it works as intended but I have a use case where I might have to loop the Promise

function getJSON(url) {
    return new Promise(function(resolve, reject){
        var xhr = new XMLHttpRequest();
        xhr.open('GET', url);
        xhr.onreadystatechange = handleResponse;
        xhr.onerror = function(error) { reject(error); }
        xhr.send();

        function handleResponse(){
            if(xhr.readyState === 4){
                if( xhr.status === 200){
                    var results = JSON.parse(xrh.responseText);
                    resolve(results);
                } else {
                    reject(this.statusText);
                }
            }
        };
    });
}

ajaxPromise = getJSON('http://url_a')
.then(getJSON(http://url_b))
.then(doSomethingWithBothResponses);

for example...

I need to run a ajax request to got query a table for its column names get that info and then query another table for its column names and add both responses to an array called column names.

Answer 1 · 2017-08-15T01:14:04Z

August 15, 2017 1:14am

If you don't need the response from the from your first query to make your second you can use Promise.all() to make both simultaneously. Then you'd have the data from both:

Promise.all( [getJSON('http://url_a'), getJSON('http://url_b')] )
    .then(doSomethingWithBothResponses);    // the function is passed an array of both results

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John Weland

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Promises Loop

1 Answer

Seth Kroger

Seth Kroger

John Weland

John Weland