如何在collection.find（{}）中返回值

Question

var shortLinks = [];

Link.find({}, function (err, links) {

    if (err) {
        console.log(err);

    } else {

        links.map(link => {
            shortLinks.push(link.shortLink);
        });

    }
    console.log(shortLinks);//shortLinks has values, all okey
});

console.log(shortLinks); //shortLinks is empty

i need to use shortLinks after Link.find({}) but array is empty. Need to return shortLinks.

Answer 1

Callbacks. The function(err, links) is called asynchronously, so shortLinks isn't populated until that function is called. Your bottom console.log is being called first, due to how callbacks work.

https://developer.mozilla.org/en-US/docs/Mozilla/js-ctypes/Using_js-ctypes/Declaring_and_Using_Callbacks

Answer 2

need to use promise:

const shortLinks = [];

const getShortLinks = Link.find({}, function (err, links) {

    if (err) {
        console.log(err);

    } else {

        links.map(link => {
            shortLinks.push(link.shortLink);
        });

    }
});

getShortLinks.then(function(links){
    console.log(shortLinks);
}, function(err){
    console.log(err);
});