Node.js Wait for redis client.get before send json object

Question

res.json(data) is called before redis client get data from server... How can i wait for data before send json object?

app.get('/api/player/:name', function(req, res) {
    var name = req.params.name;

    var data = {
        "connected": 0,
        "health": 0,
        "armour": 0
    };

    readClient.get(name + '.connected', function(err, value) {
        data.connected = value;
    });

    readClient.get(name + '.health', function(err, value) {
        data.health = value;
    });

    readClient.get(name + '.armour', function(err, value) {
        data.armour = value;
        console.log(data);
    });

    console.log(data);

    res.json(data);
});

Martín Zaragoza · Accepted Answer · 2018-09-14 13:56:09Z

1

Well, redis calls are async. That means that every query call must receive a callback function that shall be called once the query completes injecting data an errors. In order to send res.json when all data is ready then you must do something like:

app.get('/api/player/:name', function(req, res) {
    var name = req.params.name;

    var data = {
        "connected": 0,
        "health": 0,
        "armour": 0
    };

    var promises = [];

    promises.push( new Promise( function(resolve,reject) {
        readClient.get(name + '.connected', function(err, value) {
            if(err) { reject(err); }
            resolve(value);
        });
    } ) );

    promises.push( new Promise( function(resolve,reject) {
        readClient.get(name + '.health', function(err, value) {
            if(err) { reject(err); }
            resolve(value);
        });
    } ) );

    promises.push( new Promise( function(resolve,reject) {
        readClient.get(name + '.armour', function(err, value) {
            if(err) { reject(err); }
            resolve(value);
        });
    } ) );

    Promise.all(promises).then( function(values) {
        console.log(values);
        data.connected = values[0];
        data.health = values[1];
        data.armour = values[2];
        res.json(data);
    } ).catch(handleError);
});

function handleError(err) {
    res.status(501); 
    res.send({msg:err.message});
}

I'd recommend working with await and Promises however, but this is a good starting point.

Hope this helps

edited Sep 14, 2018 at 13:56

answered Sep 14, 2018 at 13:11

Martín Zaragoza

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3 Comments

Vincenzo Over a year ago

Ok this work! Can you show me how do that with async/await and Promises?

Martín Zaragoza Over a year ago

Ok. Could you pleas mark the answer as correct? (click on the green "tick" sign)

Martín Zaragoza Over a year ago

There you go. I've changed my answer to show how to solve it with promises and vanilla javascript. A more elegant solution would be using ECMASCRIPT6 with lambdas. But I don't know if you're familiarized with it

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