實現值

該 Promise.resolve 靜態方法可以用來值包裝成承諾。

let resolved = Promise.resolve(2);
resolved.then(value => {
    // immediately invoked
    // value === 2
});

如果 value 已經是一個承諾， Promise.resolve 只是重鑄它。

let one = new Promise(resolve => setTimeout(() => resolve(2), 1000));
let two = Promise.resolve(one);
two.then(value => {
    // 1 second has passed
    // value === 2
});

事實上，value 可以是任何可以的（定義 then 方法的物件，其工作方式與規範相容的承諾一樣）。這允許 Promise.resolve 將不受信任的第三方物件轉換為受信任的第一方 Promises。

let resolved = Promise.resolve({
    then(onResolved) {
        onResolved(2);
    }
});
resolved.then(value => {
    // immediately invoked
    // value === 2
});

該 Promise.reject 靜態方法返回一個承諾，其立即與給定 reason 拒絕。

let rejected = Promise.reject("Oops!");
rejected.catch(reason => {
    // immediately invoked
    // reason === "Oops!"
});