Javascript小白经典题型(一)

function sayHi() {
  console.log(name)
  console.log(age)
  var name = ‘Lydia‘
  let age = 21
}

sayHi()

for (var i = 0; i < 3; i++) {
  setTimeout(() => console.log(i), 1)
}

for (let i = 0; i < 3; i++) {
  setTimeout(() => console.log(i), 1)
}

const shape = {
  radius: 10,
  diameter() {
    return this.radius * 2
  },
  perimeter: () => 2 * Math.PI * this.radius
}

shape.diameter()
shape.perimeter()

+true;
!"Lydia";

const bird = {
  size: ‘small‘
}

const mouse = {
  name: ‘Mickey‘,
  small: true
}

let c = { greeting: ‘Hey!‘ }
let d

d = c
c.greeting = ‘Hello‘
console.log(d.greeting)

let a = 3
let b = new Number(3)
let c = 3

console.log(a == b)
console.log(a === b)
console.log(b === c)

class Chameleon {
  static colorChange(newColor) {
    this.newColor = newColor
    return this.newColor
  }

  constructor({ newColor = ‘green‘ } = {}) {
    this.newColor = newColor
  }
}

const freddie = new Chameleon({ newColor: ‘purple‘ })
freddie.colorChange(‘orange‘)

let greeting
greetign = {} // Typo!
console.log(greetign)

function bark() {
console.log(‘Woof!‘)
}

bark.animal = ‘dog‘

function Person(firstName, lastName) {
  this.firstName = firstName;
  this.lastName = lastName;
}

const member = new Person("Lydia", "Hallie");
Person.getFullName = function () {
  return `${this.firstName} ${this.lastName}`;
}

console.log(member.getFullName());

function Person(firstName, lastName) {
  this.firstName = firstName
  this.lastName = lastName
}

const lydia = new Person(‘Lydia‘, ‘Hallie‘)
const sarah = Person(‘Sarah‘, ‘Smith‘)

console.log(lydia)
console.log(sarah)

function sum(a, b) {
  return a + b
}

sum(1, ‘2‘)

let number = 0
console.log(number++)
console.log(++number)
console.log(number)

function getPersonInfo(one, two, three) {
console.log(one)
console.log(two)
console.log(three)
}

const person = ‘Lydia‘
const age = 21

getPersonInfo`${person} is ${age} years old`

function checkAge(data) {
  if (data === { age: 18 }) {
    console.log(‘You are an adult!‘)
  } else if (data == { age: 18 }) {
    console.log(‘You are still an adult.‘)
  } else {
    console.log(`Hmm.. You don‘t have an age I guess`)
  }
}

checkAge({ age: 18 })

function getAge(...args) {
  console.log(typeof args)
}

getAge(21)

function getAge() {
  ‘use strict‘
  age = 21
  console.log(age)
}

getAge()

const sum = eval(‘10*10+5‘)

sessionStorage.setItem(‘cool_secret‘, 123)

var num = 8
var num = 10

console.log(num)

const obj = { 1: ‘a‘, 2: ‘b‘, 3: ‘c‘ }
const set = new Set([1, 2, 3, 4, 5])

obj.hasOwnProperty(‘1‘)
obj.hasOwnProperty(1)
set.has(‘1‘)
set.has(1)

const obj = { a: ‘one‘, b: ‘two‘, a: ‘three‘ }
console.log(obj)

for (let i = 1; i < 5; i++) {
  if (i === 3) continue
  console.log(i)
}

String.prototype.giveLydiaPizza = () => {
  return ‘Just give Lydia pizza already!‘
}

const name = ‘Lydia‘

name.giveLydiaPizza()

const a = {}
const b = { key: ‘b‘ }
const c = { key: ‘c‘ }

a[b] = 123
a[c] = 456

console.log(a[b])

const foo = () => console.log(‘First‘)
const bar = () => setTimeout(() => console.log(‘Second‘))
const baz = () => console.log(‘Third‘)

bar()
foo()
baz()

<div onclick="console.log(‘first div‘)">
  <div onclick="console.log(‘second div‘)">
    <button onclick="console.log(‘button‘)">
      Click!
    </button>
  </div>
</div>

<div onclick="console.log(‘div‘)">
  <p onclick="console.log(‘p‘)">
    Click here!
  </p>
</div>

const person = { name: ‘Lydia‘ }

function sayHi(age) {
  console.log(`${this.name} is ${age}`)
}

sayHi.call(person, 21)
sayHi.bind(person, 21)

function sayHi() {
  return (() => 0)()
}

typeof sayHi()

0
new Number(0)
(‘‘)
(‘ ‘)
new Boolean(false)
undefined

console.log(typeof typeof 1)

const numbers = [1, 2, 3]
numbers[10] = 11
console.log(numbers)

(() => {
  let x, y
  try {
    throw new Error()
  } catch (x) {
    (x = 1), (y = 2)
    console.log(x)
  }
  console.log(x)
  console.log(y)
})()

[[0, 1], [2, 3]].reduce(
  (acc, cur) => {
    return acc.concat(cur)
  },
  [1, 2]
)

!!null
!!‘‘
!!1

setInterval(() => console.log(‘Hi‘), 1000)

[...‘Lydia‘]

function* generator(i) {
  yield i;
  yield i * 2;
}

const gen = generator(10);

console.log(gen.next().value);
console.log(gen.next().value);

const firstPromise = new Promise((res, rej) => {
  setTimeout(res, 500, "one");
});

const secondPromise = new Promise((res, rej) => {
  setTimeout(res, 100, "two");
});

Promise.race([firstPromise, secondPromise]).then(res => console.log(res));

let person = { name: "Lydia" };
const members = [person];
person = null;

console.log(members);

const person = {
  name: "Lydia",
  age: 21
};

for (const item in person) {
  console.log(item);
}

console.log(3 + 4 + "5");

const num = parseInt("7*6", 10);

[1, 2, 3].map(num => {
  if (typeof num === "number") return;
  return num * 2;
});