Promise.resolve

Promise.resolve(Promise<any>|any value) -> Promise

Create a promise that is resolved with the given value. If value is already a trusted Promise, it is returned as is. If value is not a thenable, a fulfilled Promise is returned with value as its fulfillment value. If value is a thenable (Promise-like object, like those returned by jQuery's $.ajax), returns a trusted Promise that assimilates the state of the thenable.

This can be useful if a function returns a promise (say into a chain) but can optionally return a static value. Say, for a lazy-loaded value. Example:

var someCachedValue;

var getValue = function() {
    if (someCachedValue) {
        return Promise.resolve(someCachedValue);
    }

    return db.queryAsync().then(function(value) {
        someCachedValue = value;
        return value;
    });
};

Another example with handling jQuery castable objects ($ is jQuery)

Promise.resolve($.get("http://www.google.com")).then(function() {
    //Returning a thenable from a handler is automatically
    //cast to a trusted Promise as per Promises/A+ specification
    return $.post("http://www.yahoo.com");
}).then(function() {

}).catch(function(e) {
    //jQuery doesn't throw real errors so use catch-all
    console.log(e.statusText);
});