setTimeout的遞歸函數

Question

我使用遞歸函數從外部源獲取數據，處理它並在必要時進行其他調用。

我需要在連續調用這個外部源之前暫停。

在調用我的「最終」函數之前，如何確保從外部資源獲得所有結果？

function showAll(results) { 
    console.log('All done, time for doing something else with results') 
    console.log(results) 
} 

function checkName(person) { 
    console.log('checking name of ' + person.name) 
    if (person.name === 'Julie') return true 
} 

function checkPersons(url) { 
     // Do something here to get new data from an external source 
    var data = { 
     // 'goAgain': https://newUrl.com, 
     'results': [ 
      {name: 'Bob', age: 21}, 
      {name: 'Frank', age: 15, go: 1}, 
      {name: 'Julie', age: 12} 
     ] 
    } 

    var persons = data.results 
    var results = [] 

    persons.forEach(function(person, i) { 
     if (person.age >= 18) { 
      console.log('do not need to check name of ' + person.name) 
      results.push(person) 
     } else { 
      setTimeout(function() { 
       if (checkName(person)) { 
        console.log('Julie is ' + person.name) 
        results.push(person) 
       } 
      }, 5000 * i) 
     }   
    }) 

    if (data.goAgain) { 
     // Go back and call the function again to get the 
     // next set of results from external source 
     // checkPersons(goAgain) 
     console.log('Calling the function again to get more results if necessary') 
    } else { 
     // But, checkName is still running because of setTimeout 
     // so results doesn't yet have everything we need 
     showAll(results) 
    } 
} 

checkPersons('https://someurl.com') 

https://jsfiddle.net/nicholasduffy/28Lpsgbj/3/

do not need to check name of Bob 
// No, clearly not all done because we haven't checked Frank or Julie yet 
(index):27 All done, time for doing something else with results 
// Just Bob 
(index):28 [Object] 
(index):32 checking name of Frank 
(index):32 checking name of Julie 
(index):57 Julie is Julie 
// Now I really want results 

Answer 1

您需要處理等待的異步操作。一個好方法是使用Promises。此外，即使您不需要等待setTimeout，最好也可以像處理那樣處理所有。這使得您的流量更容易維護：

var promises = persons.map(function(person, i) { 
    return new Promise(function(resolve, reject) { 
     if (person.age >= 18) { 
      console.log('do not need to check name of ' + person.name) 
      results.push(person); 
      return resolve(); 
     } 
     setTimeout(function() { 
      if (checkName(person)) { 
       console.log('Julie is ' + person.name) 
       results.push(person); 
      } 
      resolve(); 
     }, 5000 * i) 
    }); 
}) 

Promise.all(promises) 
    .then(function() { 
     if (data.goAgain) { 
      // Go back and call the function again to get the 
      // next set of results from external source 
      // checkPersons(goAgain) 
      console.log('Calling the function again to get more results if necessary') 
     } else { 
      // But, checkName is still running because of setTimeout 
      // so results doesn't yet have everything we need 
      showAll(results) 
     } 
    });