javascript - Callback after end of asynchronous recursive function

Question

The function below prints Chrome bookmarks in a folder recursively. How could I alter the below function to call another function after the final recursive loop is processed? chrome.bookmarks.getChildren() is asynchronous which makes it difficult to know when the function is done processing everything.

Thanks.

    for (var i = 0; i < foldersArray.length; i++) {
        // The loop makes several calls with different folder IDs.
        printBookmarks(foldersArray[i]);  
    }

    // I'd like any code here to be run only after the above has 
    //finished processing    

    function printBookmarks(id) {
        chrome.bookmarks.getChildren(id, function(children) {
           children.forEach(function(bookmark) { 
               console.debug(bookmark.title);
               printBookmarks(bookmark.id);
           });
        });
    }

EDIT: Sorry, I don't think I was clear in the initial code example. I've updated the code to show the problem I'm having with the asynchronous function by calling the function multiple times. I'd like any code after the printBookmarks function calls to wait for all the printBookmarks functions to finish processing.

Answer 1

Your asynchronous method instances may all be executing at once, and you don't know how many there will be beforehand. So, you'll have to keep count and then use a callback when the last asynchronous method is done.

for (var i = 0; i < foldersArray.length; i++) {
    // The loop makes several calls with different folder IDs.
    printBookmarks(foldersArray[i], thingsToDoAfter);
}

function thingsToDoAfter() {
    // I'd like any code here to be run only after the above has 
    // finished processing.
}

var count = 0;

function printBookmarks(id, callback) {
    count++;
    chrome.bookmarks.getChildren(id, function(children) {
        children.forEach(function(bookmark) { 
            console.debug(bookmark.title);
            printBookmarks(bookmark.id, callback);
        });
        count--;
        if (count === 0 && callback)
            callback();
    });
}