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Javascript – Force an async method to stop running it's code

Is there a way to force an async method to stop running? Or is there a simple way to add support to stop running an async method?

I have this code that a user can start by clicking a start button:

async runTests() {
      await this.test1();
      await this.test2();
      await this.test3();
      await this.test4();
      await this.test5();
      await this.test6();
      await this.test7();
      await this.test8();
      await this.test9();
      await this.test10();
}

But now I need a way to stop it.

Is there a way to cancel this call or to exit out of it midway?

I would love something like,

window.cancelAsyncFunction(this.runTest);

Note: Typescript converts async calls into I believe some pseudo async JavaScript so I believe it’s possible to manually cancel it somehow but there would be benefits to having a native call if one exists.

Here is the code generated by Typescript:

var __extends = (this && this.__extends) || (function () {
    var extendStatics = function (d, b) {
        extendStatics = Object.setPrototypeOf ||
            ({ __proto__: [] } instanceof Array && function (d, b) { d.__proto__ = b; }) ||
            function (d, b) { for (var p in b) if (Object.prototype.hasOwnProperty.call(b, p)) d[p] = b[p]; };
        return extendStatics(d, b);
    };
    return function (d, b) {
        if (typeof b !== "function" && b !== null)
            throw new TypeError("Class extends value " + String(b) + " is not a constructor or null");
        extendStatics(d, b);
        function __() { this.constructor = d; }
        d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
    };
})();
var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
    function adopt(value) { return value instanceof P ? value : new P(function (resolve) { resolve(value); }); }
    return new (P || (P = Promise))(function (resolve, reject) {
        function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
        function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
        function step(result) { result.done ? resolve(result.value) : adopt(result.value).then(fulfilled, rejected); }
        step((generator = generator.apply(thisArg, _arguments || [])).next());
    });
};
var __generator = (this && this.__generator) || function (thisArg, body) {
    var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g;
    return g = { next: verb(0), "throw": verb(1), "return": verb(2) }, typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
    function verb(n) { return function (v) { return step([n, v]); }; }
    function step(op) {
        if (f) throw new TypeError("Generator is already executing.");
        while (g && (g = 0, op[0] && (_ = 0)), _) try {
            if (f = 1, y && (t = op[0] & 2 ? y["return"] : op[0] ? y["throw"] || ((t = y["return"]) && t.call(y), 0) : y.next) && !(t = t.call(y, op[1])).done) return t;
            if (y = 0, t) op = [op[0] & 2, t.value];
            switch (op[0]) {
                case 0: case 1: t = op; break;
                case 4: _.label++; return { value: op[1], done: false };
                case 5: _.label++; y = op[1]; op = [0]; continue;
                case 7: op = _.ops.pop(); _.trys.pop(); continue;
                default:
                    if (!(t = _.trys, t = t.length > 0 && t[t.length - 1]) && (op[0] === 6 || op[0] === 2)) { _ = 0; continue; }
                    if (op[0] === 3 && (!t || (op[1] > t[0] && op[1] < t[3]))) { _.label = op[1]; break; }
                    if (op[0] === 6 && _.label < t[1]) { _.label = t[1]; t = op; break; }
                    if (t && _.label < t[2]) { _.label = t[2]; _.ops.push(op); break; }
                    if (t[2]) _.ops.pop();
                    _.trys.pop(); continue;
            }
            op = body.call(thisArg, _);
        } catch (e) { op = [6, e]; y = 0; } finally { f = t = 0; }
        if (op[0] & 5) throw op[1]; return { value: op[0] ? op[1] : void 0, done: true };
    }
};

And the method that has been transpiled:

    MyClass.prototype.runTests = function () {
        return __awaiter(this, void 0, void 0, function () {
            return __generator(this, function (_a) {
                switch (_a.label) {
                    case 0: return [4 /*yield*/, this.test1()];
                    case 1:
                        _a.sent();
                        return [4 /*yield*/, this.test2()];
                    case 2:
                        _a.sent();
                        return [4 /*yield*/, this.test3()];
                    // ... trimmed out more cases
                    case 3:
                        _a.sent();
                        this.updateStatus("Tests complete!");
                        return [2 /*return*/];
                }
            });
        });
    };

Sleep method that is mentioned in the comments:

   sleep(ms) {
      return new Promise(resolve => setTimeout(resolve, ms))
   }

Calling sleep:

await this.sleep(10);
Tags:

2

Answers


  1. 0

    You can iterate your tests and stop with a class variable:

    class Test {
  constructor(){
    for(let i=1;i<=10;i++){
      this[`test${i}`] = () => new Promise(r=>setTimeout(r, 250)); 
    }
  }
  async runTests() {
     this.running = true;
     const tests = Array.from({length:10}, (_, i) => this[`test${i+1}`]);
     let i = 0;
     for(const test of tests){
        console.log(`running test ${++i}`);
        await test();
        if(!this.running){
          return;
        }
     }   
  }
  stop(){
    this.running = false;
  }
}

const test = new Test;
test.runTests();
    <button onclick="test.stop()">STOP</button>

    A more sophisticated approach would be to use AbortController which you can cancel fetch with for example:

    class Test {
  constructor(){
    for(let i=1;i<=10;i++){
      this[`test${i}`] = async (id, signal) => {
        try{
          const r = await fetch('https://jsonplaceholder.typicode.com/todos/' + id, {signal});
          return r.json();
        }catch(e){
          if(e instanceof DOMException && e.name==='AbortError'){
            console.log(`fetch aborted`);
            return null;
          }
          throw e;
        }
      };
    }
  }
  async runTests({signal}) {
     let running = true;
     signal.addEventListener('abort', () => running = false);
     const tests = Array.from({length:10}, (_, i) => this[`test${i+1}`]);
     let i = 0;
     for(const test of tests){
        console.log(`running test ${++i}`);
        console.log(`result:`, JSON.stringify(await test(i, signal)));
        if(!running){
          return;
        }
     }   
  }
}

const test = new Test;
const ctrl =  new AbortController;
test.runTests(ctrl);
    <button onclick="ctrl.abort()">STOP</button>
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  2. 0

    If your async code consists of fetch calls, you can use an AbortController to cancel the request.

    Otherwise when you create your promise, you’d need to expose a way to resolve or reject it externally.

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