CODEWITHSUNDEEP
node.jspromisebluebird
Sebastian-Laurenţiu Plesciuc
Sebastian-Laurenţiu Plesciuc

Reputation: 2472

Bluebird Promise Warning: .then only accepts functions but was passed

Using "bluebird": "^3.4.6" :

var Promise = require('bluebird');

Promise.config({
    warnings: true,
    longStackTraces: true,
    cancellation: true,
    monitoring: true
});


function getPromise1(param1, param2) {
    return new Promise( (resolve, reject) => { 
        console.log(param1, param2); 
        resolve();
    } );
}

function getPromise2(param1, param2) {
    return new Promise( (resolve, reject) => { 
        console.log(param1, param2);
        resolve();
    } );
}


function mainFunc(param1, param2) {
    getPromise1(param1, param2)
        .then(getPromise2(param1, param2));
}

mainFunc("param1", "param2");

When I run it, I get :

$ node index.js
param1 param2
param1 param2
(node:95984) Warning: .then() only accepts functions but was passed: [object Object]

How can I modify this piece of code to do the same thing without the warning? Is this warning pertinent or is it just a heads-up for the developer?

EDIT: Yes. I understand the text of the warning, i.e. .then expects a function when it actually gets a Promise object from the getPromise2 function. Nevertheless, the promise gets called. (helpful downvotes)

My predicament is how to chain promises in such a way that a new Promise will be called in the then function after the first promise executes.

Upvotes: 5

Views: 3403

Answers (2)

jfriend00
jfriend00

Reputation: 707218

The key is that you have to pass a function to .then(). You were executing your function immediately and passing the returned result from that function (which was a promise). So, you can create your own anonymous wrapper function as in Bergi's answer or you can use .bind() as in:

function mainFunc(param1, param2) {
    return getPromise1(param1, param2).then(getPromise2.bind(null, param1, param2));
}

.bind() creates the wrapper function for you and allows you to specify the arguments you want preprended to the argument list when the function is actually called at a later time.

Upvotes: 2

Bergi
Bergi

Reputation: 664327

The getPromise2() call immediately creates the promise; it then is ignored being passed to then instead of a callback. To actually chain them, you'd need to use

function mainFunc(param1, param2) {
    return getPromise1(param1, param2).then(function(promise1result) {
        return getPromise2(param1, param2);
    });
}

Upvotes: 5

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