How to run database queries synchronously in javascript

Question

let positionSettings = require('setting');

function getSetting(element) {
    let setting;
    positionSettings.find({element: element}, function (err,docs) {
        console.log(docs[0].current); // output the value
        setting = docs[0].current;
    });
    return setting;
}

$(document).on("click", "#save" , function(e) {
    console.log(getSetting("abc")); // Output undefined
});

Why is the getSetting() function returning undefined. How can I achieve it.

score 2 · Accepted Answer · answered May 11 '18 at 19:28

2

Because it's an async function, you can't mix async and sync functions this way, try something like this:

let positionSettings = require('setting');

function getSetting(element, callback) {
    positionSettings.find({element: element}, (err,docs) => {
        let setting;
        console.log(docs[0].current); // output the value
        setting = docs[0].current;
        callback(setting);
    });
}

$(document).on("click", "#save" , (e) => {
    getSetting("abc", (setting) => {
       console.log(setting);
    });
});

The fact is that you can't be sure that the data will be avaible after the function call, the only place that you have this sure is inside the callback.

And just a hint, use arrow functions to declare anonymous functions.

answered May 11 '18 at 19:28

Gabriel Carneiro

643
5
16

It doesn't matter which syntax you use for functions, except in cases where `this` is involved (and as long as you don't try to run arrow functions directly on an old browser). – David Knipe May 11 '18 at 20:00
The hint was just about design pattern and use arrow functions on this cases avoids problems with `this`. – Gabriel Carneiro May 11 '18 at 20:05
Thanks @GabrielCarneiro it worked :) – Narayan Choudhary May 12 '18 at 05:48

How to run database queries synchronously in javascript

1 Answers1