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HTML 

              
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CSS
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JS 

              
                /**
 * Data that similates a tree of folders with items in them.
 */
const data = {
	"items": [
		{
			"type": "folder",
			"title": "Folder 1",
			"items": [
				{
					"type": "folder",
					"title": "Folder 1.1",
					"items": [
						{
							"type": "link",
							"title": "Folder 1.1 | Item 1"
						},
						{
							"type": "link",
							"title": "Folder 1.1 | Item 2"
						},
						{
							"type": "link",
							"title": "Folder 1.1 | Item 3"
						},
						{
							"type": "folder",
							"title": "Folder 1.1.1",
							"items": [
								{
									"type": "link",
									"title": "Folder 1.1.1 | Item 1"
								},
								{
									"type": "link",
									"title": "Folder 1.1.1 | Item 2"
								}
							]
						}
					]
				},
				{
					"type": "folder",
					"title": "Folder 1.2",
					"items": [
						{
							"type": "folder",
							"title": "Folder 1.2.1",
							"items": [
								{
									"type": "link",
									"title": "Folder 1.2.1 | Item 1"
								},
								{
									"type": "link",
									"title": "Folder 1.2.1 | Item 2"
								},
								{
									"type": "link",
									"title": "Folder 1.2.1 | Item 3"
								}
							]
						},
						{
							"type": "link",
							"title": "Folder 1.2 | Item 1"
						},
						{
							"type": "link",
							"title": "Folder 1.2 | Item 2"
						},
						{
							"type": "link",
							"title": "Folder 1.2 | Item 3"
						},
						{
							"type": "folder",
							"title": "Folder 1.2.2",
							"items": [
								{
									"type": "link",
									"title": "Folder 1.2.2 | Item 1"
								},
								{
									"type": "link",
									"title": "Folder 1.2.2 | Item 2"
								}
							]
						},
						{
							"type": "folder",
							"title": "Folder 1.2.3",
							"items": [
								{
									"type": "link",
									"title": "Folder 1.2.3 | Item 1"
								},
								{
									"type": "link",
									"title": "Folder 1.2.3 | Item 2"
								},
								{
									"type": "link",
									"title": "Folder 1.2.3 | Item 3"
								},
								{
									"type": "folder",
									"title": "Folder 1.2.3.1",
									"items": [
										{
											"type": "link",
											"title": "Folder 1.2.3.1 | Item 1"
										},
										{
											"type": "link",
											"title": "Folder 1.2.3.1 | Item 2"
										}
									]
								},
								{
									"type": "link",
									"title": "Folder 1.2.3 | Item 4"
								}
							]
						},
						{
							"type": "link",
							"title": "Folder 1.2 | Item 4"
						},
						{
							"type": "link",
							"title": "Folder 1.2 | Item 5"
						}
					]
				}
			]
		},
		{
			"type": "folder",
			"title": "Folder 2",
		}
	]
};


/**
 * Counter for generating IDs.
 */
let idCounter = 0;


/**
 * Store the results so we can check at the end.
 */
let store = [];





const testyMcTestFace = {

	/**
	 * Entry point to run the tests.
	 */
	run() {

		this.main().then(() => {
			console.log("run(): DONE!");

			console.log("--- store ---");
			console.log(store);
		});
		
	},





	/**
	 * Start processing the tree of data here
	 */
	main() 
	{
		let promises = [];

		//-- Process first level of folders (i.e. the "trunk").
		for (var i = 0; i < data.items.length; i++) {
			var dataItem = data.items[i];

			promises.push(this.executeTrunkFolder(dataItem));
		}

		
		let promise = new Promise(function(resolve, reject) {
			//-- Exectute once all the trunk promises have been resolved (or rejected).
			//	 Calling resolve() or reject() here completes the process and tells the run()
			//	 function
			Promise.all(promises)
			.then((data) => {
				console.log("trunk(): All promises successfully completed.", data);
				resolve("trunk(): All promises successfully completed.", data);
			})
			.catch((e) => {
				console.log("trunk(): Reject caught.", e);
				reject("trunk(): Reject caught.", e);
			});

		});

		return promise;
	},



	/**
	 * Process a first level folder off the trunk.
	 */
	executeTrunkFolder(item)
	{
		const _this = this;

		let promise = new Promise(function(resolve, reject) {

			_this.asyncFunction(item, { ID: 0}).then((resultItem) => {
				//-- Process sub-folders/items of this folder.
	
				_this.processItems(item, resultItem).then(() => {
					//-- All sub-items have successfully processed
					resolve("executeTrunkFolder(): Items resolved. item=" + resultItem.ID + "|" + resultItem.type + "|" + resultItem.title);
				}).catch( () => {
					reject("reject(): Items resolution failed. item=" + resultItem.ID + "|" + resultItem.type + "|" + resultItem.title);
				});
	
			});

		});

		return promise;
	},



	/**
	 * Process all items in a folder. Add each item and sub-folder to the `store`.
	 */
	processItems(folder, parentFolder) 
	{
		const _this = this;

		let promises = [];

		let totalItems = 0;
		if (folder.items != undefined) totalItems = folder.items.length;

		console.log("--------------------");
		console.log("processItems(" + parentFolder.title + "): folder.title=" + folder.title + " | " + totalItems + " items.");


		if (totalItems == 0) 
		{
			// Nothing to process, so resolve immediately
			console.log("processItems(" + parentFolder.title + "): No children");
			
			let promise = new Promise(function (resolve, reject) {
				resolve("processItems(" + parentFolder.title + "): No children");
			});

			return promise;
		}
		else 
		{
			for (var i = 0; i < folder.items.length; i++) 
			{
				const dataItem = folder.items[i];

				if (dataItem.type == "folder") {
					//-- Process a sub-folder. 
					//	 Process it via a helper-function so `dataItem` us not changed before code in the helpers finishes execution.
					console.log("processItems(" + parentFolder.title + "): dataItem=" + dataItem.type + "|" + dataItem.title);

					promises.push(_this.executeFolder(dataItem, parentFolder));
				}
				else 
				{
					//-- Process an item in the folder.
					console.log("processItems(" + parentFolder.title + "): item=" + dataItem.type + "|" + dataItem.title);

					promises.push(_this.executeItem(dataItem, parentFolder));
				}
			}
		}


		let promise = new Promise(function (resolve, reject) {
			//-- Once all items have been processed in this folder, alert the the calling function.
			Promise.all(promises)
			.then(() => {
				console.log("processItems(" + parentFolder.title + "): All promises successfully completed.");
				resolve("processItems(" + parentFolder.title + "): All promises successfully completed.");
			})
			.catch((e) => {
				console.log("processItems(" + parentFolder.title + "): Reject caught.");
				reject("processItems(" + parentFolder.title + "): Reject caught.");
			});
		});

		return promise;
	},



	/**
	 * Process a `folder` type item. 
	 * Call an async function that adds the item to the store.
	 */
	executeFolder(item, parentFolder) 
	{
		const _this = this;

		console.log("executeFolder(): ", item, parentFolder);

		let promise = new Promise(function (resolve, reject) {

			_this.asyncFunction(item, parentFolder)
			.then((resultItem) => {
				_this.processItems(item, resultItem).then(() => {
					// Successfully performed the action
					console.log("executeFolder.then(" + parentFolder.title + "):", resultItem);
					resolve("executeFolder.then(" + parentFolder.title + "): New folder ID=" + resultItem.ID);
				});
			})
			.catch( (e) => {
				// Failed to perform the action.
				console.log("executeFolder.catch(" + parentFolder.title + "):", e);
				reject("executeFolder.cathch(" + parentFolder.title + "):");
			});

		});

		return promise;
	},



	/**
	 * Process an `item` type item. 
	 * Call an async function that adds the item to the store.
	 */
	executeItem(item, parentFolder)
	{
		const _this = this;

		console.log("executeItem(): ", item, parentFolder);

		let promise = new Promise(function (resolve, reject) {

			_this.asyncFunction(item, parentFolder)
			.then((resultItem) => {
				// Successfully performed the action
				console.log("executeItem.then(" + parentFolder.title + "):", resultItem);
				resolve("executeItem.then(" + parentFolder.title + "):");
			})
			.catch( (e) => {
				// Failed to perform the action
				console.log("executeItem.catch(" + parentFolder.title + "):", e);
				reject("executeItem.cathch(" + parentFolder.title + "): New item ID=" + resultItem.ID);
			});

		});

		return promise;
	},
	




	asyncFunction(item, parentFolder) {
		console.log("asyncFunction(): ", item, parentFolder);

		// Wait 500ms then add the supplied item to the store
		let promise = new Promise(function (resolve, reject) {
			setTimeout(() => {
				idCounter = idCounter + 1;

				item.ID = idCounter;

				store.push(
				{
					item: item,
					parent: parentFolder
				});

				resolve(item);
			}, 500);
		});

		return promise;
	}

}


testyMcTestFace.run();
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