回调中的Javascript范围

Question

I have a method with a callback inside of nodeJS where I'm trying to set a value in the outer function that can be returned with the result of the data that is being passed in the callback to a mongoose call:

'use strict';

var mongoose = require('mongoose')
    ,Alert = mongoose.model('Alert');

exports.getAllAlerts = function() {
    var result = [];
    Alert.find({}, function(err, alerts) {
        if(err) {
            console.log('exception while fetching alerts');
        }
        if(alerts) {
            result = alerts;
            console.log('result: ' + result);
        }
    });
    return result;
}

How can I set the value of result[] with the value of alerts that's coming back in the mongoose callback?

Thanks in advance

Answer 1

Most likely, find() runs asyncronously, in that case, you will always return an empty Array , because at the time you return the value, its not defined nor assigned.

You would need to rewrite your .getAllAlerts() method so it allows a callback function for itself, like

exports.getAllAlerts = function( cb ) {
    Alert.find({}, function(err, alerts) {
        if(err) {
            console.log('exception while fetching alerts');
        }

        if(alerts) {
            if( typeof cb === 'function' ) {
                cb( alert || [ ] );
            }
        }
    });
}

...and you would use that in a way like

YourModule.getAllAlerts(function( alerts ) {
    console.log( alerts );
});