JavaScript 中断请求几种方案详解

new Promise((resolve, reject) => {
    setTimeout(() => {
        resolve('result');
    });
}).then(res => {
    // 达到某种条件,return一个pending状态的Promise实例,以中断调用链
    if (res === 'result') {
        return new Promise(() => {});
    }
    console.log(res); // 不打印
}).then(() => {
    console.log('then不执行'); // 不打印
}).catch(() => {
    console.log('catch不执行'); // 不打印
}).finally(() => {
    console.log('finally不执行'); // 不打印
});

const request = new Promise((resolve, reject) => {
  setTimeout(() => {
    resolve('收到服务端数据')
  }, Math.random() * 3000)
})

const timeoutReject = (p1, timeout = 2000) => {
    const p2 = new Promise((resolve, reject) => {
        setTimeout(() => {
            reject('网络超时');
        }, timeout);
    });
    return Promise.race([p1, p2]);
};

timeoutReject(request).then(res => {
    console.log(res);
}).catch(err => {
    console.log(err);
});

function abortWrapper(p1) {
    let abort;
    const p2 = new Promise((resolve, reject) => {
        abort = reject;
    });
    // 如果没有resolve或reject,p2的状态永远是pending
    const p = Promise.race([p1, p2]);
    p.abort = abort;
    return p;
}

const req = abortWrapper(request);
req.then(res => {
    console.log(res);
}).catch(err => {
    console.log(err);
});

setTimeout(() => {
    // 手动调用req.abort,将p2的状态改变为rejected
    req.abort('手动中断请求');
}, 2000);

let stream1$ = new Observable(observer => {
    let timeout = setTimeout(() => {
        observer.next('observable timeout');
    }, 2000);

    return () => {
        clearTimeout(timeout);
    }
});
let disposable = stream1$.subscribe(value => console.log(value));
setTimeout(() => {
    disposable.unsubscribe();
}, 1000);

import axios from 'axios';
const CancelToken = axios.CancelToken;
const source = CancelToken.source();

axios.get('/user/12345', {
  cancelToken: source.token
}).catch(function (thrown) {
  if (axios.isCancel(thrown)) {
    console.log('Request canceled', thrown.message);
  } else {
    // handle error
  } 
});

source.cancel('Operation canceled by the user.');

import axios from 'axios';
const CancelToken = axios.CancelToken;

// 创建一个变量如 cancel 用于存储这个中断某个请求的方法
let cancel;

axios.get('/user/12345', {
  cancelToken: new CancelToken(function executor(c) {
    cancel = c; // 将参数 c 赋值给 cancel
  })
});

// 判断 cancel 是否为函数,确保 axios 已实例化一个CancelToken
if (typeof cancel === 'function') {
    cancel();
    cancel = null;
}

'use strict';

var Cancel = require('./Cancel');

/**
 * A `CancelToken` is an object that can be used to request cancellation of an operation.
 *
 * @class
 * @param {Function} executor The executor function.
 */
function CancelToken(executor) {
  if (typeof executor !== 'function') {
    throw new TypeError('executor must be a function.');
  }

  var resolvePromise;
  this.promise = new Promise(function promiseExecutor(resolve) {
    resolvePromise = resolve;
  });

  var token = this;
  executor(function cancel(message) {
    if (token.reason) {
      // Cancellation has already been requested
      return;
    }

    token.reason = new Cancel(message);
    resolvePromise(token.reason);
  });
}

/**
 * Throws a `Cancel` if cancellation has been requested.
 */
CancelToken.prototype.throwIfRequested = function throwIfRequested() {
  if (this.reason) {
    throw this.reason;
  }
};

/**
 * Returns an object that contains a new `CancelToken` and a function that, when called,
 * cancels the `CancelToken`.
 */
CancelToken.source = function source() {
  var cancel;
  var token = new CancelToken(function executor(c) {
    cancel = c;
  });
  return {
    token: token,
    cancel: cancel
  };
};

module.exports = CancelToken;

if (config.cancelToken) {
  // Handle cancellation
  config.cancelToken.promise.then(function onCanceled(cancel) {
    if (!request) {
      return;
    }

    request.abort();
    reject(cancel);
    // Clean up request
    request = null;
  });
}