How to efficiently handle multiple asynchronous requests in Tampermonkey and determine the continuation or termination of control requests based on conditions?

This article discusses efficiently handling multiple asynchronous requests in Tampermonkey scripts and determines the continuation or termination of control requests based on conditions. This is very practical in scenarios where data needs to be fetched from multiple URLs and make decisions based on the data.

Problem Description: The Tampermonkey script needs to obtain data from multiple URLs and make conditional judgments based on these data. If a specific condition is met, the subsequent request is stopped; otherwise, the next request continues.

Challenge: Using the loop method of gm_xmlhttpRequest directly will execute all requests in sequence and cannot be stopped immediately after the conditions are met.

Solution: This article provides two solutions, namely sequential requests and concurrent requests, both of which can effectively terminate subsequent requests after the conditions are met.

Scheme 1: Sequential requests (using Promise and recursion)

This plan initiates requests in turn and makes conditional judgments after each request is completed. If the condition is satisfied, it terminates recursively; otherwise, continue to the next request.

 function promise1() { return new Promise(resolve => setTimeout(() => resolve({data: '123'}), 2000)); }
function promise2() { return new Promise(resolve => setTimeout(() => resolve({data: '#234'}), 2000)); }
function promise3() { return new Promise(resolve => setTimeout(() => resolve({data: '1'}), 2000)); }

function mainRequest(promises) {
  return new Promise(resolve => {
    let i = 0;
    function nextRequest() {
      if (i === promises.length) { resolve('all do not meet the criteria'); return; }
      const request = promises[i]();
      i ;
      request.then(result => {
        if (result.data.indexOf('#') > -1) { resolve(result.data); }
        else { nextRequest(); }
      }).catch(() => nextRequest()); // Handle error}
    nextRequest();
  });
}

mainRequest([promise3, promise2, promise1]).then(result => console.log('result', result));

Solution 2: Concurrent requests (using Promise.all and conditional judgment)

This scheme initiates all requests at the same time, and uses Promise.all to wait for all requests to complete. Then, the traversal result is verified for conditional judgment, and then the first result that meets the condition is found and subsequent processing is stopped.

 function Promise1() { return new Promise(resolve => setTimeout(() => resolve({data: '#123'}), Math.random() * 1000)); }
function Promise2() { return new Promise(resolve => setTimeout(() => resolve({data: '#234'}), Math.random() * 1000)); }
function Promise3() { return new Promise(resolve => setTimeout(() => resolve({data: '#1'}), Math.random() * 1000)); }

function mainRequest(promises) {
  return Promise.all(promises.map(p => p())).then(results => {
    for (let i = 0; i  -1) { return { successIndex: i, data: results[i].data }; }
    }
    return 'No request matching the criteria was found';
  });
}

mainRequest([Promise3, Promise2, Promise1]).then(result => console.log('result', result));

Summary: Both solutions achieve the goal of stopping subsequent requests after the conditions are met. Which solution to choose depends on the specific requirements: sequential requests save resources, concurrent requests are faster but consume more resources. It should be noted that gm_xmlhttpRequest itself does not provide the function of canceling the request, so in the concurrency scheme, we achieve the effect of "stop" by ignoring the subsequent results after finding the result that meets the condition. In actual applications, adjustments need to be made according to specific APIs and conditions.

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