数组扁平化
例：
输入：[[1, 2, 2], [3, 4, 5, 5], [6, 7, 8, 9, [11, 12, [12, 13, [14]]]], 10]
输出：[ 1, 2, 2, 3, 4, 5, 5, 6, 7, 8, 9, 11, 12, 12, 13, 14, 10 ]
方法一
var newArr = []
function flatten(arr) {
for (var i = 0; i < arr.length; i++) {
if (Object.prototype.toString.call(arr[i]) === '[object Array]') {
flatten(arr[i])
} else {
newArr.push(arr[i])
}
}
}
方法二
var flatten = function(array) {
return array.reduce(function(previous, val) {
if (Object.prototype.toString.call(val) !== '[object Array]') {
return previous.push(val), previous
}
return Array.prototype.push.apply(previous, flatten(val)), previous
}, [])
}
方法三
function flatten(arr) {
while (arr.some(item => Array.isArray(item))) {
arr = [].concat(...arr)
}
return arr
}
实现 map
Array.prototype.myMap = function(callback) {
var arr = []
for (var i = 0; i < this.length; i++) {
var item = callback(this[i], i)
arr.push(item)
}
return arr
}
实现 bind
Function.prototype.myBind = function(context) {
var self = this
var args = [].slice.call(arguments, 1)
return function() {
return self.apply(context, args.concat(arguments))
}
}
实现一个简单的字符串模版引擎
效果如下：
var str = 'hello, i am <%=user%>, from <%=location%>'
var compiled = template(str)
compiled({ user: 'zzw', location: 'ez' }) // 'hello, i am zzw, from ez'
代码：
function template(temp) {
var temp = temp
return function(obj) {
var reg = /<%=(\w+)%>/
var result
console.log(temp)
while ((result = reg.exec(temp))) {
var key = result[1]
var value = obj[key]
temp = temp.replace(result[0], value)
}
return temp
}
}
实现深克隆
function deepClone(obj) {
var result,
oClass = isClass(obj)
//确定result的类型
if (oClass === 'Object') {
result = {}
} else if (oClass === 'Array') {
result = []
} else {
return obj
}
for (key in obj) {
var copy = obj[key]
if (isClass(copy) == 'Object' || isClass(copy) == 'Array') {
result[key] = arguments.callee(copy) //递归调用
} else {
//如果为基本数据类型
result[key] = obj[key]
}
}
return result
}
//返回传递给他的任意对象的类
function isClass(o) {
if (o === null) return 'Null'
if (o === undefined) return 'Undefined'
return Object.prototype.toString.call(o).slice(8, -1)
}
深克隆变形题目：将 json 字符串所有键名第一个首字母转为大写(考虑嵌套对象)
例：输入
{"hyKey":"myValue","q23":"123","arr":[1,2,3],"obj":{"name":"zzw"},"null":null}
输出:
{"HyKey":"myValue","Q23":"123","Arr":[1,2,3],"Obj":{"Name":"zzw"},"Null":null}
function toUpperCase1(obj) {
var result,
oClass = isClass(obj)
if (oClass === 'Object') {
result = {}
} else if (oClass === 'Array') {
result = []
} else {
return obj
}
for (var key in obj) {
var copy = obj[key]
if (isClass(copy) == 'Object' || isClass(copy) == 'Array') {
result[key.slice(0, 1).toUpperCase() + key.slice(1)] = arguments.callee(
copy
)
} else {
result[key.slice(0, 1).toUpperCase() + key.slice(1)] = obj[key]
}
}
return result
}
事件委托
实现：给定一个 ul 列表，里面有若干个 li 标签，li 里面也嵌套了若干标签，要求点击标签，弹出当前 li 在 ul 中的位置.
Document
var ul = document.getElementById('ul')
ul.addEventListener('click', function(e) {
// 事件委托
var e = e.target
while (e.nodeName != 'LI') {
e = e.parentNode
}
var childrenArr = [].slice.apply(ul.children)
var liArr = childrenArr.filter(function(child) {
if (child.nodeName == 'LI') {
return child
}
})
console.log(liArr.indexOf(e))
})
输出字符串中所有的叠词
输入： '晴川历历汉阳树，芳草萋萋鹦鹉洲'
输出： [ '历历', '萋萋' ]
function rw(str) {
var result = []
for (var i = 1; i < str.length; i++) {
if (str[i] == str[i - 1]) {
result.push(str.slice(i - 1, i + 1))
}
}
return result
}
实现一个 add 函数
执行如下：
add(1, 2); // 3
add(1)(2); // 3
add(1, 2, 3)(1, 4)(2, 2)(1) // 16
function add() {
var sum = 0
var arr = [].slice.call(arguments)
for (var i = 0; i < arr.length; i++) {
sum += arr[i]
}
var temp = function() {
var arr = [].slice.call(arguments)
for (var i = 0; i < arr.length; i++) {
sum += arr[i]
}
return temp
}
temp.toString = function() {
return sum
}
return temp
}
一个考察了 this/变量提升/构造函数返回值/运算符优先级的题目
function Foo() {
getName = function() {
alert(1)
} // 没有var
return this
}
Foo.getName = function() {
alert(2)
}
Foo.prototype.getName = function() {
alert(3)
}
var getName = function() {
alert(4)
}
function getName() {
alert(5)
}
/* 写出输出 */
Foo.getName() // 2
getName() // 4 => 变量提升
Foo().getName() // 1 => 函数调用this指向 window.getName()
getName() // 1
new Foo.getName() // 2 => new (Foo.getName)() 运算符优先级
new Foo().getName() // 3 => (new Foo()).getName() 构造函数返回值
new new Foo().getName() // 3 => new Foo().getName()
实现一个 LazyMan
// 实现一个LazyMan，可以按照以下方式调用:
LazyMan(“Hank”)
// 输出: Hi! This is Hank!
LazyMan(“Hank”).sleep(10).eat(“dinner”)
// 输出:
// Hi! This is Hank!
// 等待10秒..
// Wake up after 10
// Eat dinner~
LazyMan(“Hank”).eat(“dinner”).eat(“supper”)
// 输出:
// Hi This is Hank!
// Eat dinner~
// Eat supper~
LazyMan(“Hank”).sleepFirst(5).eat(“supper”)
// 输出:
// 等待5秒
// Wake up after 5
// Hi This is Hank!
// Eat supper
以此类推。
答案
function _LazyMan(name) {
const self = this
this.taskqueue = []
console.log(`Hi, This is ${name}`)
setTimeout(() => {
self.next()
}, 0)
}
_LazyMan.prototype.next = function() {
const fn = this.taskqueue.shift()
fn && fn()
}
_LazyMan.prototype.sleep = function(time) {
const self = this
const fn = function() {
setTimeout(() => {
console.log(`Wake up after ${time}`)
self.next()
}, time * 1000)
}
this.taskqueue.push(fn)
return this
}
_LazyMan.prototype.eat = function(name) {
const self = this
const fn = function() {
console.log(`Eat ${name}`)
self.next()
}
this.taskqueue.push(fn)
return this
}
_LazyMan.prototype.sleepFirst = function(time) {
const self = this
const fn = function() {
setTimeout(() => {
console.log(`Wake up after ${time}`)
self.next()
}, time * 1000)
}
this.taskqueue.unshift(fn)
return this
}
function LazyMan(name) {
return new _LazyMan(name)
}
实现一个 compose 方法，要求如下
function fun1(ctx, next) {
ctx.count++
console.log(ctx.count)
next()
}
function fun2(ctx, next) {
ctx.count++
console.log(ctx.count)
setTimeout(function() {
next()
}, 1000)
}
function fun3(ctx, next) {
ctx.count++
console.log(ctx.count)
next()
}
compose([fun1, fun2, fun3])({ count: 1 }) // 2 3 4
答案
function compose(arr) {
return function(ctx) {
const next = function() {
const fn = arr.shift()
fn && fn(ctx, next)
}
next()
}
}
实现一个 composite 方法，要求如下
function add(a, b) {
return a + b
}
function square(a) {
return a * a
}
function plusOne(c) {
return c + 1
}
var addSquareAndPlusOne = composite(add, square, plusOne)
console.log(addSquareAndPlusOne(1, 2)) // 10
答案:
function composite(...fns) {
return function(...args) {
return fns.reduce((accu, curr) => {
return typeof accu === 'function' ? curr(accu(...args)) : curr(accu)
})
}
}