在递归异步函数中承诺 [英] Promises in recursive asynchronous functions

问题描述

我想要一个铬合金书签并找到它的父母，一直到父书签文件夹。

下面的函数用于获取给定书签的第一个父项。

 <$ c $ b $ function getParent（bookmark）{
 var promise = new Promise（function（resolve，reject）{
 chrome.bookmarks.get（bookmark.parentId，function（nodes）{
 resolve （节点[0]）; 
}）; 
}）; 
返回承诺; 
} 
  

我无法获得所有书签父母。下面的功能不起作用，但它应该显示我在找什么。

 函数getParents（书签，父母）{
 var parents = parents || []; 
 var promise; 
 $ b $ getParent（书签）.then（函数（父）{
 if（parent.parentId =='0'）{
 parents.push（parent）; 
 promise = Promise.resolve（parents）; 
} else {
 parents.push（parent）; 
 getParents（parent，parents）; 
} 
}） ; 
返回承诺; 
} 
  

我想我真正的问题是：你如何得到承诺在递归中工作异步功能？

或者如果您有更好的方式来做到这一点，那也可以。 .then 回调或其他承诺的最终值：

 函数getParents（书签，父母）{
 var父母=父母|| []; 
 
 return getParent（bookmark）.then（function（parent）{
 parents.push（parent）; 
 return parent.parentId =='0'？parents：getParents（父母，父母）; 
}）; 
} 
  

请参阅 http://www.html5rocks.com/en/tutorials/es6/promises/#toc-chaining

I want to take a chrome bookmark and find its parents, all the way up to the parent bookmark folder.

The function below works for getting the first parent of the given bookmark.

function getParent(bookmark) {
  var promise = new Promise(function(resolve, reject) {
    chrome.bookmarks.get(bookmark.parentId, function(nodes) {
      resolve(nodes[0]);
    });
  });
  return promise;
}

I'm having trouble getting all of the bookmarks parents. The function below doesn't work but it should show what I'm looking for.

function getParents(bookmark, parents) {
  var parents = parents || [];
  var promise;

  getParent(bookmark).then(function(parent) {
    if (parent.parentId == '0') {
      parents.push(parent);
      promise = Promise.resolve(parents);
    } else {
      parents.push(parent);
      getParents(parent, parents);
    }
  });
  return promise;
}

I guess my real question is: how do you get promises to work in recursive asynchronous functions?

Or if you have a better way of doing this, that works too.

解决方案

Simply return the promise returned by .then and either return the final value from the .then callback, or another promise:

function getParents(bookmark, parents) {
  var parents = parents || [];

  return getParent(bookmark).then(function(parent) {
    parents.push(parent);
    return parent.parentId == '0' ? parents : getParents(parent, parents);
  });
}

See http://www.html5rocks.com/en/tutorials/es6/promises/#toc-chaining

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