$.when()
終止時,第一個承諾,你通過它拒絕。你無法得到所有被拒絕的承諾。您可以將其與其他代碼一起使用來跟蹤所有故障。
這裏有一個$.settle()
是等待所有承諾你傳遞它是解決或拒絕,並返回PromiseInspection對象的數組,從中可以知道哪些解決和拒絕,以及他們的解決值或拒絕的理由是:
(function() {
function isPromise(p) {
return p && (typeof p === "object" || typeof p === "function") && typeof p.then === "function";
}
function wrapInPromise(p) {
if (!isPromise(p)) {
p = $.Deferred().resolve(p);
}
return p;
}
function PromiseInspection(fulfilled, val) {
return {
isFulfilled: function() {
return fulfilled;
}, isRejected: function() {
return !fulfilled;
}, isPending: function() {
// PromiseInspection objects created here are never pending
return false;
}, value: function() {
if (!fulfilled) {
throw new Error("Can't call .value() on a promise that is not fulfilled");
}
return val;
}, reason: function() {
if (fulfilled) {
throw new Error("Can't call .reason() on a promise that is fulfilled");
}
return val;
}
};
}
// pass either multiple promises as separate arguments or an array of promises
$.settle = function(p1) {
var args;
if (Array.isArray(p1)) {
args = p1;
} else {
args = Array.prototype.slice.call(arguments);
}
return $.when.apply($, args.map(function(p) {
// make sure p is a promise (it could be just a value)
p = wrapInPromise(p);
// Now we know for sure that p is a promise
// Make sure that the returned promise here is always resolved with a PromiseInspection object, never rejected
return p.then(function(val) {
return new PromiseInspection(true, val);
}, function(reason) {
// convert rejected promise into resolved promise by returning a resolved promised
// One could just return the promiseInspection object directly if jQuery was
// Promise spec compliant, but jQuery 1.x and 2.x are not so we have to take this extra step
return wrapInPromise(new PromiseInspection(false, reason));
});
})).then(function() {
// return an array of results which is just more convenient to work with
// than the separate arguments that $.when() would normally return
return Array.prototype.slice.call(arguments);
});
}
// simpler version that just converts any failed promises
// to a resolved value of what is passed in, so the caller can just skip
// any of those values in the returned values array
// Typically, the caller would pass in null or 0 or an empty object
$.settleVal = function(errorVal, p1) {
var args;
if (Array.isArray(p1)) {
args = p1;
} else {
args = Array.prototype.slice.call(arguments, 1);
}
return $.when.apply($, args.map(function(p) {
p = wrapInPromise(p);
return p.then(null, function(err) {
return wrapInPromise(errorVal);
});
}));
}
})();
用法:
$.settle(arrayOfPromises).then(function(results) {
// results is an array of PromiseInspection objects and you can
// tell which are resolved and which are rejected
results.forEach(function(item, index) {
if (item.isFulfilled()) {
console.log("promise #" + index + " is fulfilled with value: ", item.value(););
} else {
console.log("promise #" + index + " is rejected with reason: ", item.reason(););
}
});
});
使用jQuery是這不可能?這是否會在IE11中工作,因爲我將Promises看成是ES6的東西? – user183872