Javascript Promises Chained

promiseBulk.js

 function gimmeAPromiseWith(x) {
    return new Promise(function(resolve, reject) {
        console.log(`started calculation of ${x}`);
        setTimeout(function() {
            resolve(x);
            console.log(`finished calculation of ${x}`);
        }.bind(this), 10);
    });
}


const whatwhatwhat = 'chain';

switch (whatwhatwhat) {

    case 'parallel':

        const promises = [
            gimmeAPromiseWith(1),
            gimmeAPromiseWith(2),
            gimmeAPromiseWith(3),
        ];
        Promise.all(promises).then(console.log); // [ 1, 2, 3 ]
        Promise.all(promises).then(console.log); // [ 1, 2, 3 ]
        break;


    case 'chain':

        const xs = [1, 2, 3];
        xs.reduce(function(promise, x) {
            return promise.then(v => gimmeAPromiseWith(x));
        }, Promise.resolve()).then(console.log); // 3
        break;

}