js
1. Promise.race
返回第一个完成（成功或失败）的 Promise：
jsApplyCancelconst PromiseRace = (promises) => {
return new Promise((resolve, reject) => {
const arr = Array.from(promises);
// 空数组的话永远不会 resolve 或 reject
if (arr.length === 0) {
return; // 保持 pending 状态
}
for (let i = 0; i < arr.length; i++) {
Promise.resolve(arr[i])
.then(resolve) // 第一个成功就 resolve
.catch(reject); // 第一个失败就 reject
}
});
};
// TypeScript 版本
function PromiseRace<T>(promises: Promise<T>[]): Promise<T> {
return new Promise((resolve, reject) => {
const arr = Array.from(promises);
if (arr.length === 0) {
return;
}
for (let i = 0; i < arr.length; i++) {
Promise.resolve(arr[i])
.then(resolve)
.catch(reject);
}
});
}
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2. Promise.allSettled
等待所有 Promise 完成，无论成功失败都返回结果：
jsApplyCancelconst PromiseAllSettled = (promises) => {
return new Promise((resolve) => {
const arr = Array.from(promises);
const len = arr.length;
if (len === 0) {
resolve([]);
return;
}
let count = 0;
const results = [];
for (let i = 0; i < len; i++) {
Promise.resolve(arr[i])
.then((value) => {
results[i] = {
status: 'fulfilled',
value: value
};
if (++count === len) {
resolve(results);
}
})
.catch((reason) => {
results[i] = {
status: 'rejected',
reason: reason
};
if (++count === len) {
resolve(results);
}
});
}
});
};
// TypeScript 版本
type SettledResult<T> =
| { status: 'fulfilled'; value: T }
| { status: 'rejected'; reason: any };
function PromiseAllSettled<T>(
promises: Promise<T>[]
): Promise<SettledResult<T>[]> {
return new Promise((resolve) => {
const arr = Array.from(promises);
const len = arr.length;
if (len === 0) {
resolve([]);
return;
}
let count = 0;
const results: SettledResult<T>[] = [];
for (let i = 0; i < len; i++) {
Promise.resolve(arr[i])
.then((value) => {
results[i] = { status: 'fulfilled', value };
if (++count === len) resolve(results);
})
.catch((reason) => {
results[i] = { status: 'rejected', reason };
if (++count === len) resolve(results);
});
}
});
}
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3. Promise.any
返回第一个成功的 Promise，所有都失败才 reject：
jsApplyCancelconst PromiseAny = (promises) => {
return new Promise((resolve, reject) => {
const arr = Array.from(promises);
const len = arr.length;
if (len === 0) {
reject(new AggregateError([], 'All promises were rejected'));
return;
}
let rejectionCount = 0;
const errors = [];
for (let i = 0; i < len; i++) {
Promise.resolve(arr[i])
.then(resolve) // 任意一个成功就直接 resolve
.catch((error) => {
errors[i] = error;
if (++rejectionCount === len) {
// 所有都失败才 reject
reject(new AggregateError(errors, 'All promises were rejected'));
}
});
}
});
};
// TypeScript 版本
function PromiseAny<T>(promises: Promise<T>[]): Promise<T> {
return new Promise((resolve, reject) => {
const arr = Array.from(promises);
const len = arr.length;
if (len === 0) {
reject(new AggregateError([], 'All promises were rejected'));
return;
}
let rejectionCount = 0;
const errors: any[] = [];
for (let i = 0; i < len; i++) {
Promise.resolve(arr[i])
.then(resolve)
.catch((error) => {
errors[i] = error;
if (++rejectionCount === len) {
reject(new AggregateError(errors, 'All promises were rejected'));
}
});
}
});
}
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4. Promise.resolve
将值转换为 resolved 的 Promise：
jsApplyCancelconst PromiseResolve = (value) => {
// 如果已经是 Promise，直接返回
if (value && typeof value.then === 'function') {
return value;
}
// 如果是 thenable 对象
if (value && typeof value === 'object' && typeof value.then === 'function') {
return new Promise((resolve, reject) => {
value.then(resolve, reject);
});
}
// 普通值直接 resolve
return new Promise((resolve) => {
resolve(value);
});
};
// TypeScript 版本
function PromiseResolve<T>(value: T | PromiseLike<T>): Promise<T> {
if (value && typeof (value as any).then === 'function') {
return Promise.resolve(value);
}
return new Promise((resolve) => {
resolve(value as T);
});
}
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5. Promise.reject
创建一个 rejected 的 Promise：
jsApplyCancelconst PromiseReject = (reason) => {
return new Promise((_, reject) => {
reject(reason);
});
};
// TypeScript 版本
function PromiseReject<T = never>(reason?: any): Promise<T> {
return new Promise((_, reject) => {
reject(reason);
});
}
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6. Promise.prototype.finally
无论成功失败都会执行的回调：
jsApplyCancelconst addFinally = (PromisePrototype) => {
PromisePrototype.finally = function(callback) {
return this.then(
(value) => {
return Promise.resolve(callback()).then(() => value);
},
(reason) => {
return Promise.resolve(callback()).then(() => {
throw reason;
});
}
);
};
};
// 使用方法
addFinally(Promise.prototype);
// TypeScript 接口扩展
declare global {
interface Promise<T> {
finally(onfinally?: (() => void) | null): Promise<T>;
}
}
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完整测试用例
jsApplyCancel// Promise.race 测试
console.log('=== Promise.race 测试 ===');
const raceTest = [
new Promise(resolve => setTimeout(() => resolve('fast'), 100)),
new Promise(resolve => setTimeout(() => resolve('slow'), 500))
];
PromiseRace(raceTest).then(console.log); // 输出: 'fast'
// Promise.allSettled 测试
console.log('=== Promise.allSettled 测试 ===');
const settledTest = [
Promise.resolve(1),
Promise.reject('error'),
Promise.resolve(3)
];
PromiseAllSettled(settledTest).then(console.log);
// 输出: [
// { status: 'fulfilled', value: 1 },
// { status: 'rejected', reason: 'error' },
// { status: 'fulfilled', value: 3 }
// ]
// Promise.any 测试
console.log('=== Promise.any 测试 ===');
const anyTest1 = [
Promise.reject('error1'),
Promise.resolve('success'),
Promise.reject('error2')
];
PromiseAny(anyTest1).then(console.log); // 输出: 'success'
const anyTest2 = [
Promise.reject('error1'),
Promise.reject('error2'),
Promise.reject('error3')
];
PromiseAny(anyTest2).catch(console.error); // 输出: AggregateError
// Promise.resolve 测试
console.log('=== Promise.resolve 测试 ===');
PromiseResolve(42).then(console.log); // 输出: 42
PromiseResolve(Promise.resolve('hello')).then(console.log); // 输出: 'hello'
// Promise.reject 测试
console.log('=== Promise.reject 测试 ===');
PromiseReject('something wrong').catch(console.error); // 输出: something wrong
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核心区别总结
API成功条件失败条件特点Promise.all全部成功任意失败快速失败，保序返回Promise.race第一个完成第一个失败竞速模式Promise.allSettled总是成功从不失败容错模式，返回状态Promise.any任意成功全部失败容错模式，第一个成功Promise.resolve立即成功-值转 PromisePromise.reject-立即失败创建失败 Promise
这些实现帮你深入理解 Promise 的并发控制和状态管理机制！每个 API 都有其特定的使用场景。