Tips

You have to run the following code in the browser, for running from editor like VS Code can't get the wrong window or global value

Syntax

var obj = {
  name: '123',
  getName: function() {
    console.log(this.name)
  }
}

var getName = obj.getName
var getName1 = obj.getName.bind(obj)

getName()
getName1()

function f1() {
  var a = 222

  function f2() {
    console.log(a)
  }

  nAdd = function() {
    a += 1
  }

  return f2
}

var obj = f1()
obj()

nAdd()
obj()

var length = 10
function fn() {
  console.log('fn: ' + this.length)
}

var obj1 = {
  length: 5,
  method: function(fn) {
    fn()
    arguments[0]()
  }
}

obj1.method(fn, 1)

var a = 2
function get(a) {
  console.log('first time: ' + a)
  var a = 1
  function a() {}
  console.log('second time: ' + a)
}

get(1)

var a = 1
function init(a) {
  console.log(a)
  var a = 2
  function a() {}
  console.log(a)
}

init(1)

var length = 10
function getLength() {
  console.log(this.length)
}

var obj = {
  length: 5,
  getLength: function() {
    console.log(this.length)
  }
}

getLength()
obj.getLength()

var obj = {
  name: 'zs',
  age: 18,
  friends: ['Kate', 'Bob', 'Mike'],
  hobby: {
    hobby1: 'codes',
    hobby2: 'piano'
  }
}

function copy(oldObj) {
  var newObj = {}
  for (var key in oldObj) {
    newObj[key] = oldObj[key]
  }
  return newObj
}

var obj2 = copy(obj)
console.log(obj2.friends === obj.friends)

var obj3 = Object.assign(obj)
console.log(obj3.friends === obj.friends)

var a = 1

function logA() {
  console.log(this)
  console.log(a)
  var a = 2
  console.log(this.a)
  this.a = 3
}

logA()
new logA()

Promise

new Promise(resolve => {
  console.log(1)
  resolve()
  console.log(2)
}).then(() => {
  console.log(3)
})

new Promise(() => {
  console.log(4)
}).then(() => {
  console.log(5)
})

const original = Promise.resolve(2)
new Promise(resolve => {
  resolve(original)
  Promise.resolve().then(() => Promise.resolve().then(() => console.log(1)))
  console.log(4)
}).then(t => console.log(t))
console.log(3)

async function foo() {
  console.log('1')
  await bar()
  console.log('3')
}

function bar() {
  return new Promise(resolve => {
    console.log('5')
    resolve()
    console.log('7')
  })
}

;(async () => {
  await foo()
})()

const promise = Promise.resolve(2)

new Promise(resolve => {
  resolve(promise)
  Promise.resolve().then(() => Promise.resolve().then(() => console.log(1)))
  console.log(4)
}).then(t => console.log(t))

console.log(3)