const nums = [1, 2, 3];
const strs = Array.from('est');

nums.push(6);
nums.push(4, 9);
strs.unshift('t');

nums.length;                     // 6
nums[nums.length - 1];           // 9
strs[0];                         // 't'
strs[2];                         // 's'

nums.slice(1, 3);                // [2, 3]
nums.map(n => n * 2);            // [2, 4, 6, 12, 8, 18]
nums.filter(n => n % 2 === 0);   // [2, 6, 4]
nums.reduce((a, n) => a + n, 0); // 25

strs.reverse();                  // ['t', 's', 'e', 't']
strs.join('');                   // 'test'

const nums = new Set([1, 2, 3]);

nums.add(4);
nums.add(1);
nums.add(5);
nums.add(4);

nums.size;                       // 5
nums.has(4);                     // true

nums.delete(4);
nums.has(4);                     // false

[...nums];                       // [1, 2, 3, 5]

nums.clear();
nums.size;                       // 0

const items = new Map([
  [1, { name: 'John' }],
  [2, { name: 'Mary' }]
]);

items.set(4, { name: 'Alan' });
items.set(2, { name: 'Jeff' });

items.size;                      // 3
items.has(4);                    // true
items.get(2);                    // { name: 'Jeff' }

items.delete(2);
items.size;                      // 2

[...items.keys()];               // [1, 4]
[...items.values()];             // [{ name: 'John' }, { name: 'Alan' }]

items.clear();
items.size;                      // 0

const MongoClient = require('mongodb').MongoClient;
const assert = require('assert');

// Connection URL
const url = 'mongodb://localhost:27017';

// Database Name
const dbName = 'myproject';

// Use connect method to connect to the server
MongoClient.connect(url, function(err, client) {
  assert.equal(null, err);
  console.log("Connected successfully to server");

  const db = client.db(dbName);

  client.close();
});

const toFixed = (n, fixed) => ~~(Math.pow(10, fixed) * n) / Math.pow(10, fixed);
// Examples
toFixed(25.198726354, 1);       // 25.1
toFixed(25.198726354, 2);       // 25.19
toFixed(25.198726354, 3);       // 25.198
toFixed(25.198726354, 4);       // 25.1987
toFixed(25.198726354, 5);       // 25.19872
toFixed(25.198726354, 6);       // 25.198726

if (process.env.NODE_ENV === "production") {
	app.use(express.static("client/build"));

	app.get("*", (req, res) => {
	res.sendFile(path.resolve(__dirname, "client", "build", "index.html"));
	});
}

const compactObject = val => {
  const data = Array.isArray(val) ? val.filter(Boolean) : val;
  return Object.keys(data).reduce(
    (acc, key) => {
      const value = data[key];
      if (Boolean(value))
        acc[key] = typeof value === 'object' ? compactObject(value) : value;
      return acc;
    },
    Array.isArray(val) ? [] : {}
  );
};

const obj = {
  a: null,
  b: false,
  c: true,
  d: 0,
  e: 1,
  f: '',
  g: 'a',
  h: [null, false, '', true, 1, 'a'],
  i: { j: 0, k: false, l: 'a' }
};
compactObject(obj);
// { c: true, e: 1, g: 'a', h: [ true, 1, 'a' ], i: { l: 'a' } }

class TreeNode {
  constructor(key, value = key, parent = null) {
    this.key = key;
    this.value = value;
    this.parent = parent;
    this.children = [];
  }

  get isLeaf() {
    return this.children.length === 0;
  }

  get hasChildren() {
    return !this.isLeaf;
  }
}

class Tree {
  constructor(key, value = key) {
    this.root = new TreeNode(key, value);
  }

  *preOrderTraversal(node = this.root) {
    yield node;
    if (node.children.length) {
      for (let child of node.children) {
        yield* this.preOrderTraversal(child);
      }
    }
  }

  *postOrderTraversal(node = this.root) {
    if (node.children.length) {
      for (let child of node.children) {
        yield* this.postOrderTraversal(child);
      }
    }
    yield node;
  }

  insert(parentNodeKey, key, value = key) {
    for (let node of this.preOrderTraversal()) {
      if (node.key === parentNodeKey) {
        node.children.push(new TreeNode(key, value, node));
        return true;
      }
    }
    return false;
  }

  remove(key) {
    for (let node of this.preOrderTraversal()) {
      const filtered = node.children.filter(c => c.key !== key);
      if (filtered.length !== node.children.length) {
        node.children = filtered;
        return true;
      }
    }
    return false;
  }

  find(key) {
    for (let node of this.preOrderTraversal()) {
      if (node.key === key) return node;
    }
    return undefined;
  }
}

const tree = new Tree(1, 'AB');

tree.insert(1, 11, 'AC');
tree.insert(1, 12, 'BC');
tree.insert(12, 121, 'BG');

[...tree.preOrderTraversal()].map(x => x.value);
// ['AB', 'AC', 'BC', 'BCG']

tree.root.value;              // 'AB'
tree.root.hasChildren;        // true

tree.find(12).isLeaf;         // false
tree.find(121).isLeaf;        // true
tree.find(121).parent.value;  // 'BC'

tree.remove(12);

[...tree.postOrderTraversal()].map(x => x.value);
// ['AC', 'AB']