现代JavaScript教程-基础知识

let a = true

alert(a)
a = String(value) // 现在是字符串形式的true

alert("6" / "2") // string会转换成number类型进行转换

Number("6") // 6
Number("你好") // NaN

Boolean(1) // true
Boolean(0) // false
Boolean("abc") // true
Boolean("") // false

let a = 1;
a = -a

let a = 1
let b = 2
alert(a + b)

+true // 1
+"" // 0
+undefined // NaN

let a = 1 + 1

let a, b, c;
a = b = c = 1

let a = 2
a += a
a *= a
a /= a
a -= a

let a = 2
let b = a++
console.log(a, b) // 3, 2

let a = 2
let b = ++a
console.log(a, b) // 3, 3

!!0 // false
!0 true

label: for(let a = 0; a < 10; a++) {
		if(a === 2) break label;
}

switch () {
    case '': {
        break;
    }
    case '': {
        break;
    }
    default: {
        break
    }     
}

function showMessage() {}

let showMessage = function() {}

function sayHi() {
		alert('Hello')
}

let fuc = sayHi;

fuc()
sayHi()

function ask(question, yes, no) {
  if (confirm(question)) yes()
  else no();
}

function showOk() {
  alert( "You agreed." );
}

function showCancel() {
  alert( "You canceled the execution." );
}

// 用法：函数 showOk 和 showCancel 被作为参数传入到 ask
ask("Do you agree?", showOk, showCancel);

function ask(question, yes, no) {
  if (confirm(question)) yes()
  else no();
}

ask("Do you agree?", function() {alert('yes')}, function() {alert("no")});