const x = 20;
let big;
if (x > 10) {
big = true;
} else {
big = false;
}
//這樣寫...
const big = x > 10 ? true : false;

if (variable1 !== null || variable1 !== undefined || variable1 !== '') {
  let variable2 = variable1;
}
// 這樣寫
const variable2 = variable1 || 'new';

let variable1;
let variable2 = variable1 || '';
console.log(variable2 === ''); // true
variable1 = 'foo';
variable2 = variable1 || '';
console.log(variable2); // foo

let x;
let y;
let x = 3;

// or 
let x, y, z = 3;

if (likeJavaScript === true)
//or
if (likeJavaScript)

let a;
if (a !== true) {
// do something ...
}
//or
let a;
if (!a) {
// do something ...
}

for (let i = 0; i < allImgs.length; i++)
//or
for (let index in allImgs)

function logArrayElements(element, index, array) {
console.log('a[' + index + ']=' + element);
}
[2, 5, 9].forEach(logArrayElements);
// logs:
// a[0] = 2
// a[1] = 5
// a[2] = 9

const obj = {x: x, y: y};
//or
const obj = {x, y};

function sayHello(name) {
console.log('Hello', name);
}
setTimeout(function() {
console.log('Loaded')
}, 2000);
list.forEach(function(item){
console.log(item)
})

//or
sayHello = name => console.log('Hello', name);
setTimeout(() => console.log('Loaded'), 2000);
list.forEach(item => console.log(item));

function calcCircumference(diameter) {
return Math.PI * diameter
}
//or
calcCircumference = diameter => (
Math.PI * diameter;
)

function volume(l, w, h) {
if (w === undefined)
    w = 3;
if (h === undefined)
    h = 4;
return l * w * h;
}
//or
volume = (l, w = 3, h = 4) => (l * w * h);
volume(2); // 24

const welcome = 'You have logged in as' + first + ' ' + last + '.';
const db = 'http://' + host + ':' + port + '/' + database;
//or
const welcome = `You have logged in as ${first} ${last}`;
const db = `http://${host}:${port}/${database}`;

const observable = require('mobx/observable');
const action = require('mobx/action');
const runInAction = require('mobx/runInAction');


const store = this.props.store;
const form = this.props.form;
const loading = this.props.loading;
const errors = this.props.errors;
const entity = this.props.entity;

//or

import {observable, action, runInAction} from 'mobx';
const {store, form, loading, errors, entity} = this.props;

const {store, form, loading, errors, entity:contact} = this.props; //通過 : 號(hào)來重命名

// Joining arrays
const odd = [1, 3, 5];
const nums = [2, 4, 6].concat(odd);


// cloning arrays
const arr = [1, 2, 3, 4];
const arr2 = arr.slice();
//or
// Joining arrays
const odd = [1, 3, 5];
const nums = [2, 4, 6, ...odd];
console.log(nums); // [2, 4, 6, 1, 3, 5]


// cloning arrays
const arr = [1, 2, 3, 4];
const arr2 = [...arr];

const odd = [1, 3, 5];
const nums = [2, ...odd, 4, 6];

const {a, b, ...z} = {a: 1, b: 2, c: 3, d: 4};
console.log(a); // 1
console.log(b); // 2
console.log(z); // {c: 3, d: 4}

function foo(bar) {
if (bar === undefined) {
throw new Error('Missing parameter!');
  }
return bar;
}
//or
mandatory = () => {
throw new Error('Missing parameter!');
}
foo = (bar = mandatory()) => {
return bar;
}

const pets = [
  {type: 'Dog', name: 'Max'},
  {type: 'Cat', name: 'Karl'},
  {type: 'Dog', name: 'Tommy'}
]
function findDog(name) {
for (let i = 0; i < pets.length; ++i) {
if (pets[i].type === 'Dog' && pets[i].name === name) {
return pets[i];
    }
  }
}
 // or
pet = pets.find(pet => pet.type === 'Dog' && pet.name === 'Tommy');
console.log(pet); // {type: 'Dog', name: 'Tommy'}

function validate(values) {
if (!values.first)
return false;
if (!values.last)
return false;
return true;
}
console.log(validate({first: 'Bruce', last: 'Wayne'})); // true

// object validation rules
const schema = {
first: {
required: true
  },
last: {
required: true
  }
}
// universal validation function
const validate = (schema, values) => {
for(field in schema) {
if (schema[field].required) {
if(!values[field]) {
return false;
      }
    }
  }
return true;
}
console.log(validate(schema, {first: 'Bruce'})); // false
console.log(validate(schema, {first: 'Bruce', last: 'Wayne'})); //true

Math.floor(4.9) === 4; // true
//or
~~4.9 === 4; //true