// WRONG
var results = [];
theArray.forEach(function(entry) {
doSomethingAsync(entry, function(result) {
results.push(result);
});
});
console.log(results); // E.g., using them, returning them, etc.
平行
var results = [];
var expecting = theArray.length;
theArray.forEach(function(entry, index) {
doSomethingAsync(entry, function(result) {
results[index] = result;
if (--expecting === 0) {
// Done!
console.log("Results:", results); // E.g., using the results
}
});
});
例子:
请注意我们如何使用 forEach 的指数,以保存结果的结果与其所涉及的输入相同的位置,即使结果从顺序中出来(因为 async 通话不一定在它们开始的顺序中完成)。
function doSomethingWith(theArray, callback) {
var results = [];
var expecting = theArray.length;
theArray.forEach(function(entry, index) {
doSomethingAsync(entry, function(result) {
results[index] = result;
if (--expecting === 0) {
// Done!
callback(results);
}
});
});
}
doSomethingWith(theArray, function(results) {
console.log("Results:", results);
});
例子:
function doSomethingWith(theArray, callback) {
var results = [];
var expecting = theArray.length;
theArray.forEach(function(entry, index) {
doSomethingAsync(entry, function(result) {
results[index] = result;
if (--expecting === 0) {
// Done!
callback(results);
}
});
});
}
doSomethingWith([1, 2, 3], function(results) {
console.log("Results:", JSON.stringify(results));
});
function doSomethingAsync(value, callback) {
console.log("Starting async operation for " + value);
setTimeout(function() {
console.log("Completing async operation for " + value);
callback(value * 2);
}, Math.floor(Math.random() * 200));
}
.as-console-wrapper { max-height: 100% !important; }
或者这里是返回承诺的版本:
function doSomethingWith(theArray) {
return new Promise(function(resolve) {
var results = [];
var expecting = theArray.length;
theArray.forEach(function(entry, index) {
doSomethingAsync(entry, function(result) {
results[index] = result;
if (--expecting === 0) {
// Done!
resolve(results);
}
});
});
});
}
doSomethingWith(theArray).then(function(results) {
console.log("Results:", results);
});
当然,如果 doSomethingAsync 传递给我们错误,我们将使用拒绝来拒绝承诺,当我们得到错误时。
function doSomethingWith(theArray) {
return Promise.all(theArray.map(function(entry) {
return doSomethingAsync(entry);
}));
}
doSomethingWith(theArray).then(function(results) {
console.log("Results:", results);
});
function doSomethingWith(theArray) {
return Promise.all(theArray.map(doSomethingAsync));
}
doSomethingWith(theArray).then(function(results) {
console.log("Results:", results);
});
系列
function doSomethingWith(theArray, callback) {
var results = [];
doOne(0);
function doOne(index) {
if (index < theArray.length) {
doSomethingAsync(theArray[index], function(result) {
results.push(result);
doOne(index + 1);
});
} else {
// Done!
callback(results);
}
}
}
doSomethingWith(theArray, function(results) {
console.log("Results:", results);
});
async function doSomethingWith(theArray) {
const results = [];
for (const entry of theArray) {
results.push(await doSomethingAsync(entry));
}
return results;
}
doSomethingWith(theArray).then(results => {
console.log("Results:", results);
});
function doSomethingWith(theArray) {
return theArray.reduce(function(p, entry) {
return p.then(function(results) {
return doSomethingAsync(entry).then(function(result) {
results.push(result);
return results;
});
});
}, Promise.resolve([]));
}
doSomethingWith(theArray).then(function(results) {
console.log("Results:", results);
});
function doSomethingWith(theArray) {
return theArray.reduce((p, entry) => p.then(results => doSomethingAsync(entry).then(result => {
results.push(result);
return results;
})), Promise.resolve([]));
}
doSomethingWith(theArray).then(results => {
console.log("Results:", results);
});
例子:
