Promise

studying_promise.js

// http://azu.github.io/promises-book/
// https://developer.mozilla.org/ja/docs/Web/JavaScript/Reference/Global_Objects/Promise

p = (name, num = 1) => {
    return new Promise((resolve, reject) => {
        console.log(`${Date.now()} - num=[${num}] name=[${name}]`);
        setTimeout(() => {
            console.log(`${Date.now()} - timeout: num=[${num}] name=[${name}]`)

            if (name) {
                resolve("hello " + name + "!");
            }
            else {
                reject("error");
            }
        }, num * 1000);
    });
}

let foo = p("a")
    .then(result => {
        console.log(result);
        return result;
    })
    .catch(result => {
        console.log(result);
        return result;
    });
setTimeout(_ => { console.log(foo) }, 2 * 1000);


Promise.all([
    p("b"),
    p("c", 2),
    // p(""),
])
    .then(result => console.log(result))
    .catch(result => console.log(result));


Promise.race([
    p("a", Math.random() * 10),
    p("b", Math.random() * 10),
    p("c", Math.random() * 10),
])
    .then(result => console.log(result))
    .catch(result => console.log(result));