开始吧,做时间的主人!
把时间分给睡眠,分给书籍,分给运动,
分给花鸟树木和山川湖海,
分给你对这个世界的热爱,
而不是将自己浪费在无聊的人和事上。
思维导图
函数
为什么需要函数
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<html lang="en"><head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title><style>span {display: inline-block;width: 100px;padding: 5px 10px;border: 1px solid pink;margin: 2px;border-radius: 5px;box-shadow: 2px 2px 2px rgba(255, 192, 203, .4);background-color: rgba(255, 192, 203, .1);text-align: center;color: hotpink;}</style>
</head><body><script>// // 1. 外层循环控制行数// for (let i = 1; i <= 9; i++) {// // 2. 里层循环控制列数// for (let j = 1; j <= i; j++) {// document.write(`<span>${j} X ${i} = ${i * j}</span>`)// }// // 换行// document.write('<br>')// }// // 1. 外层循环控制行数// for (let i = 1; i <= 9; i++) {// // 2. 里层循环控制列数// for (let j = 1; j <= i; j++) {// document.write(`<span>${j} X ${i} = ${i * j}</span>`)// }// // 换行// document.write('<br>')// }// // 1. 外层循环控制行数// for (let i = 1; i <= 9; i++) {// // 2. 里层循环控制列数// for (let j = 1; j <= i; j++) {// document.write(`<span>${j} X ${i} = ${i * j}</span>`)// }// // 换行// document.write('<br>')// }// 声明function sheet99() {for (let i = 1; i <= 9; i++) {// 2. 里层循环控制列数for (let j = 1; j <= i; j++) {document.write(`<span>${j} X ${i} = ${i * j}</span>`)}// 换行document.write('<br>')}}// 调用sheet99()sheet99()sheet99()sheet99()</script>
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代码复用,生成多个99乘法表
函数使用
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</head><body><script>// let num = 10// console.log(num)// 1. 函数的声明 function sayHi() {console.log('hi~~~')}// 2. 函数调用 函数不调用,自己不执行sayHi()sayHi()sayHi()</script>
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<html lang="en"><head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head><body><script>// 1. 求2个数的和// function getSum() {// let num1 = +prompt('请输入第一个数')// let num2 = +prompt('请输入第二个数')// console.log(num1 + num2)// }// getSum()// 2. 求 1~100 累加和function getSum() {let sum = 0for (let i = 1; i <= 100; i++) {sum += i}console.log(sum)}getSum()</script>
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函数传参
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<html lang="en"><head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head><body><script>// 2. 求 1~100 累加和// function getSum(end) { // end = 50// // console.log(end)// let sum = 0// for (let i = 1; i <= end; i++) {// sum += i// }// console.log(sum)// }// getSum(50) // 1~50// getSum(100) // 1~100function getSum(start, end) { // end = 50// 形参 形式上的参数 // console.log(end)let sum = 0for (let i = start; i <= end; i++) {sum += i}console.log(sum)}getSum(1, 50) // 调用的小括号里面 实参 - 实际的参数getSum(100, 200) // 实参 - 实际的参数</script>
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<html lang="en"><head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head><body><script>// 1. 封装函数// 给一个参数的默认值function getArrSum(arr = []) {// console.log(arr)let sum = 0for (let i = 0; i < arr.length; i++) {sum += arr[i]}console.log(sum)}getArrSum([1, 2, 3, 4, 5])getArrSum([11, 22, 33])getArrSum() // 0</script>
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函数返回值
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</head><body><script>// // 函数的返回值// function fn() {// return 20// }// // fn() 调用者 相当于执行了 fn() = 20// // return 的值返回给调用者// // console.log(fn())// // let num = prompt('请输入数字')// let re = fn()// console.log(re)// 求和函数的写法function getTotalPrice(x, y) {return x + y// return 后面的代码不会被执行}// console.log(getTotalPrice(1, 2))// console.log(getTotalPrice(1, 2))let sum = getTotalPrice(1, 2)console.log(sum)console.log(sum)function fn() {}let re = fn()console.log(re) // undefined</script>
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<html lang="en"><head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title></head><body><div></div><script>// 1. 求最大值函数// function getMax(x, y) {// return x > y ? x : y// }// let max = getMax(11, 234)// console.log(max)// // 2. 求任意数组的最大值,并且返回// function getArrValue(arr = []) {// // (1)先准备一个max变量存放数组的第一个值// let max = arr[0]// // (2) 遍历比较// for (let i = 1; i < arr.length; i++) {// if (max < arr[i]) {// max = arr[i]// }// }// // (3) 返回值// return max// }// // let max = getArrValue([1, 3, 5, 7, 9])// // let num = prompt('请输入')// let max = getArrValue([11, 3, 55, 7, 29])// console.log(max)// 3. 求任意数组的最大值和最小值,并且返回function getArrValue(arr = []) {// (1)先准备一个max变量存放数组的第一个值let max = arr[0]let min = arr[0] // 最小值// (2) 遍历比较for (let i = 1; i < arr.length; i++) {// 最大值if (max < arr[i]) {max = arr[i]}// 最小值if (min > arr[i]) {min = arr[i]}}// (3) 返回值 返回的是数组return [max, min]// return min}let newArr = getArrValue([11, 3, 55, 7, 29])console.log(`数组的最大值是: ${newArr[0]}`)console.log(`数组的最小值是: ${newArr[1]}`)</script>
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<!DOCTYPE html>
<html lang="en"><head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head><body><script>// function getSum(x, y) {// return x + y// // 返回值返回给了谁? 函数的调用者 getSum(1, 2)// // getSum(1, 2) = 3// }// // let result = getSum(1, 2) = 3// // let num = parseInt('12px')// let result = getSum(1, 2)// console.log(result)// 1. 函数名相同, 后面覆盖前面// function fn() {// console.log(1)// }// function fn() {// console.log(2)// }// fn()// 2. 参数不匹配function fn(a, b) {console.log(a + b)}// (1). 实参多余形参 剩余的实参不参与运算// fn(1, 2, 3)// (2). 实参少于形参 剩余的实参不参与运算fn(1) // 1 + undefined = NaN </script>
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作用域
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<html lang="en"><head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head><body><script>let num = 10 // 1. 全局变量console.log(num)function fn() {console.log(num)}fn()// 2. 局部变量function fun() {let str = 'pink'}console.log(str) // 错误</script>
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函数内部,第一次出现的局部变量被当做全局变量
无let变量声明关键词,甚至覆盖同名全局变量(强烈不推荐)
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<html lang="en"><head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head><body><script>// let num = 20// function fn() {// num = 10 // 全局变量来看 强烈不允许// }// fn()// console.log(num)// function fun(x, y) {// // 形参可以看做是函数的局部变量// console.log(x)// }// fun(1, 2)// console.log(x) // 错误的// let num = 10function fn() {// let num = 20function fun() {// let num = 30console.log(num)}fun()}fn()</script>
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匿名函数
第三方js文件(具名立即执行函数),担心变量名冲突:
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<html lang="en"><head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head><body><script>// age = age + 1// 1. 用户输入let second = +prompt('请输入秒数:')// 2.封装函数function getTime(t) {// console.log(t) // 总的秒数// 3. 转换// 小时: h = parseInt(总秒数 / 60 / 60 % 24)// 分钟: m = parseInt(总秒数 / 60 % 60)// 秒数: s = parseInt(总秒数 % 60) let h = parseInt(t / 60 / 60 % 24)let m = parseInt(t / 60 % 60)let s = parseInt(t % 60)h = h < 10 ? '0' + h : hm = m < 10 ? '0' + m : ms = s < 10 ? '0' + s : s// console.log(h, m, s)return `转换完毕之后是${h}小时${m}分${s}秒`}let str = getTime(second)document.write(str)console.log(h)</script>
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