Learn about promise and q in node js

Good Link to study promises in node

https://www.youtube.com/watch?v=s6SH72uAn3Q

Use-cases of promises and reasons to switch to promises
https://spion.github.io/posts/why-i-am-switching-to-promises.html

Sample program with q and promises 

const {PythonShell} =  require('python-shell');

var Q = require('q');
var Promise = require('promise');

var pk = function runPythonShell(){
return  Q.Promise(function(resolve, reject){
PythonShell.runString('x=1+1;print(x)', null, function(err , result){
if(err){
reject(err);
}else{
        console.log("result " + result);
resolve("finshed");
}

})
});
}


Q.fcall(pk)
.then(function (value4) {
    // Do something with value4
    console.log("lola next");

})
.catch(function (error) {
    // Handle any error from all above steps
    console.log("there is some error");
    console.log(error);
})
.done();