A. "string"
B. "function"
C. "object"
D. "null"
A. 输入：typeof {"x":1} 输出："object"
B. 输入：typeof 1 输出："number"
C. 输入：typeof [{x:1}] 输出："array"
D. 输入：typeof NaN 输出："number"
A. undefined
B. null
C. array
D. object
A. Boolean
B. undefined
C. Symbol
D. Array
A. 数据类型分为基本数据类型和引用数据类型
B. JavaScript一共有8种数据类型
C. Object是引用数据类型，且只存储于堆(heap)中
D. BigInt是可以表示任意精度整数的基本数据类型，存储于栈(stack)中
答案
DCADC
A. null instanceof Object
B. null === undefined
C. null == undefined
D. NaN == NaN
A. Symbol.for('a') === Symbol.for('a')
B. Symbol('a') === Symbol('a')
C. NaN === NaN
D. {} === {}
var a = 1;
var b = [];
var c = '';
var d = true;
A. (a || b) === true
B. (b && c) === true
C. (c && d) === true
D. (d || a) === true
A. T
B. F
A. console.log([] === []);
B. console.log(undefined == 0);
C. console.log(undefined == false);
D. console.log(false == '');
A. console.log("12" === 12)
B. console.log (NaN === NaN)
C. console.log (typeof(null) === typeof(window))
D. console.log ([1,2,3] === [1,2,3])
注意浏览器环境与node环境的差别，比如C选项
A. Number('a') == Number('a')
B. -1 == true
C. 3 + '2' === 5
D. ![] == ''
答案
CADADCD
A. Math.round(7.25)
B. Math.ceil(7.25)
C. round(7.25)
D. Math.rnd(7.25)
A. Math.floor(Math.random()*6)
B. Math.floor(Math.random()*10)
C. Math.floor(Math.random()*11)
D. Math.ceil(Math.random()*10)
A. Math.floor(Math.random()*6)
B. Math.floor(Math.random()*7)
C. Math. floor(Math.random()*8)
答案
A CD(注意D) C
A. T
B. F
A. match()
B. indexOf()
C. search()
D. concat()
答案
A BC
A. ｛name:"xiaoming",age,"student"｝
B. ｛"name":"xiaoming","age":"student"｝
C. ｛"xiaoming","student"｝
D. ["xiaoming","student"]
const fn = function(){}
const res = JSON.stringify(fn)
const num = 123
const res = JSON.stringify(num)
const res = JSON.stringify(NaN)
const b = true
const res = JSON.stringify(b)
A. 'function'、'123'、'NaN'、'true'
B. undefined、'123'、undefined、'true'
C. undefined、'123'、'null'、'true'
D. undefined、'123'、'null'、undefined
答案
BC
A. push
B. concat
C. sort
D. shift
A. slice
B. splice
C. sort
D. unshift
A. push
B. pop
C. shift
D. unshift
A. push
B. pop
C. unshift
D. splice
A. concat
B. splice
C. slice
D. join
A. concat
B. shift
C. filter
D. map
A. push
B. slice
C. splice
D. sort
// (1)
const newNums = Array.from(new Set(nums))
// (2)
const newNums = nums.filter((n, i) => {
return nums.indexOf(n) === i
})
// (3)
const newNums = nums.forEach((n, i) => {
return nums.indexOf(n) === i
})
// (4)
const newNums = nums.reduce((acc, n, i) => {
return [].concat(acc, nums.indexOf(n) === i ? n : []
)
})
A. (1)、(2)、(3)、(4)
B. (1)、(3)、(4)
C. (1)、(2)、(4)
D. (1)、(4)
答案
BAABB
BBC
A. 123
B. 123a
C. d123
D. 123def
A. test
B. match
C. exec
D. compile
A. str.replace(`/s*/g,""`)
B. str.replace(`/^s|s$/g,""`)
C. str.replace(`/^s*/, ""`)
D. str.replace(`/(s*$)/g, ""`)
答案
CBA
A. encodeURI
B. parseFloat
C. round
D. eval
A. 遵循严格模式："use strict"
B. 将js脚本放在页面顶部，加快渲染页面
C. 将js脚本成组打包，减少请求，尽量减少使用闭包
D. 使用非阻塞方式下载js脚本，最小化重绘(repAInt)和回流(reflow)
A. parseFloat方法：该方法将一个字符串转换成对应的小数
B. isNaN方法：该方法用于检测参数是否为数值型，如果是，返回true，否则，返回false。
C. escape方法： 该方法返回对一个字符串编码后的结果字符串
D. eval方法：该方法将某个参数字符串作为一个JavaScript执行题
A. chrome
B. Safari
C. 搜狗浏览器
D. Firefox
// A
var formatDate=getDate()
// B
var formatDate = new Date()
// C
var formatDate = function (date) {
var y = date.getFullYear();
var m = date.getMonth() + 1;
var d = date.getDate();
return y + '-' + m + '-' + d;
};
// D
var formatDate = function (date) {
var y = date.getFullYear();
var m = date.getMonth() + 1;
m = m < 10 ? '0' + m : m;
var d = date.getDate();
d = d < 10 ? ('0' + d) : d;
return y + '-' + m + '-' + d;
};
A. 需要对元素进行复杂的操作时，可以先隐藏(display:"none")，操作完成后再显示
B. 需要创建多个DOM节点时，使用DocumentFragment创建完后一次性的加入document
C. 尽量避免用table布局(table元素一旦触发回流就会导致table里所有的其它元素回流)
D. 尽量不要使用 css 属性简写，如：用border-width, border-style, border-color代替border
答案
CBBDDD
A. eval
B. Apply
C. bind
D. call
A. 在使用new实例化对象时, this指向这个实例对象
B. 将对象的方法赋值给变量A。执行A()时 该方法中的this指向这个对象。
C. 在函数定义时,this指向全局变量
D. 在浏览器下的全局范围内，this指向全局对象
A. call与apply都属于Function.prototype的一个方法，所以每个function实例都有call、apply属性
B. 两者传递的参数不同，call函数第一个参数都是要传入给当前对象的对象，apply不是
C. apply传入的是一个参数数组，也就是将多个参数组合成为一个数组传入
D. call传入的则是直接的参数列表。call 方法可将一个函数的对象上下文从初始的上下文改变为由 thisObj 指定的新对象。
答案
AAB
// (1)
function getName() {
name = 'javascript'
}
getName()
// (2)
const elements = {
button: document.getElementById('button')
};
function removeButton() {
document.body.removeChild(elements.button);
}
removeButton()
// (3)
let timer = setInterval(() => {
const node = document.querySelector('#node')
if(node) {
clearInterval(timer)
}
}, 1000);
A. (1)、(2)、(3)
B. (2)、(3)
C. (1)、(3)
D. (1)、(2)
A. 没有清理的DOM元素引用
B. 被遗忘的定时器
C. 事件侦听没有移除
D. 局部变量不用时，没有设为null
A. 增加一定的内存消耗
B. 使用不当可能会导致内存泄漏
C. 可以使用闭包模拟私有方法
D. 闭包会改动对象的原型链
答案
DDD
A. 原型链继承
B. 构造函数继承
C. 组合继承
D. 关联继承
A. T
B. F
A. 通过原型链继承的属性和对象自己定义的属性等效
B. 通过原型链可以模拟对象的私有属性
C. 在对象上访问不存在的属性时,会依次遍历整条原型链
D. 所有 JavaScript 中的对象都是位于原型链顶端的 `Object` 的实例
答案
DBC
A. jsonp
B. cookie
C. localStorage
D. sessionStorage
答案
A
A. event.preventDefault()
B. event.prevent()
C. event.drag()
D. event.drop()
A. mouseover
B. click
C. mouseleave
D. mousemove
A. stopDeafault()
B. stopPropagation()
C. preventDefault()
D. preventDefaultEven()
目标 -> 捕获 -> 冒泡
冒泡 -> 目标 -> 捕获
目标 -> 冒泡 -> 捕获
捕获 -> 目标 -> 冒泡
A. onchange：用户改变域的内容
B. onkeypress：某个键盘的键被按下或按住
C. onmousedown：某个鼠标按键被按下
D. onblur：元素获得焦点
答案
ACCDD
A. parentObj.firstChild
B. parentObj.children
C. neborNode.previousSibling
D. neborNode.siblings
A. appendChild(parentNode,newNode);
B. append(parentNode,newNode);
C. parentNode.append(newNode);
D. parentNode.appendChild(newNode);
A. Array
B. Object
C. String
D. Function
A. appendChild(parentNode,newNode);
B. append(parentNode,newNode);
C. parentNode.append(newNode);
D. parentNode.appendChild(newNode);
答案
DDBD
outline
visiblity
font-size
background-color
答案
C
A. 每隔60秒调用一次updateClock()
B. 每隔60毫秒调用一次updateClock()
C. 每隔60分钟调用一次updateClock()
D. 每分钟调用60次updateClock()
A. Geolocation.watchPosition()
B. Geolocation.getCurrentPosition()
C. Geolocation.getPosition()
D. Geolocation.Position()
A. 等待1000秒后，再弹出一个对话框
B. 等待1秒钟后弹出一个对话框
C. 每隔一秒钟弹出一个对话框
D. 语句报错,语法有问题
答案
BBC
A. 箭头函数没有原型属性
B. 箭头函数不绑定this，会捕获其所在的上下文的this值，作为自己的this值
C. 箭头函数可以作为构造函数，使用new
D. 箭头函数不绑定arguments，取而代之用rest参数解决
A. 函数体内this的指向是定义时所在的对象，而不是使用时所在的对象
B. 箭头函数内不能使用arguments对象
C. 箭头函数不能使用yield命令
D. 可以使用new创建一个箭头函数的实例
答案
CD
Promise.all([]).then((res) => {
console.log('all');
});
Promise.race([]).then((res) => {
console.log('race');
});
A. all 和 race 都会被输出
B. all 和 race 都不会被输出
C. all 会被输出，而 race 不会被输出
D. all 不会被输出，race 会被输出
A. Promise
B. Generator
C. async
D. Proxy
A. Pending
B. Pause
C. Fulfilled
D. Rejected
答案
CDB
let [a,b, c,d, e] = "hello";
A. e = "hello";
B. 其它都为undefined
C. 当中 a = "h", b = "e";
D. 语法报错
答案
C
A. push
B. concat
C. splice
D. map
A. const a = 0xa1
B. const a = 076
C. const a = 0b21
D. const a = 7e2
(1)function
(2) object
(3) null
(4) array
(5) NaN
(6) bigint
(7) regexp
(8) undefined
A. (1)、(2)、(3)、(4)、(5)、(6)、(7)、(8)
B. (1)、(2)、(3)、(8)
C. (1)、(2)、(8)
D. (1)、(2)、(6)、(8)
A. typeof 'string'
B. String('string').toString()
C. 'string'.split('').sort().join('')
D. (function(string){return string})('string')
E. JSON.parse('{"string":"string"}').string
A. parseInt(46.8) `==` parseFloat(46.8)
B. NaN `!==` NaN
C. isNaN('abc') `==` NaN
D. typeof NaN `===` 'number'
A. Array.from(A)
B. [].slice.apply(A)
C. [...A]
D. [].map.call(A, o => o)
A. null == undefined
B. null === undefined
C. null === null
D. NaN == null
E. NaN === NaN
F. Infinity + 1 !== Infinity
答案
AC ABD D ABDE BD ABCD AC
function Person() { } var person = new Person();
A. 每一个原型都有一个constructor属性指向关联的构造函数。
B. 每一个对象都有一个prototype属性。
C. Object.getPrototypeOf(person) === Person.prototype
D. person.constructor === Person
A. process.nextTick
B. promise
C. setTimeout
D. setInterval
答案
ACD AB
A. let声明的变量值和类型都可以改变
B. const声明的常量不可以改变
C. 两者都不存在变量提升，同时存在暂时性死区，只能在声明的位置后面使用
D. const可以先声明再初始化，可以后赋值
A. Promise.all在所有给定的promise都fulfilled后才返回结果
B. Promise.race在给定的promise中，某个fulfilled后才返回结果
C. promise.then的回调函数中，可以返回一个新的promise
D. 对于一个向后台获取数据已经产生结果的promise:p1，再次调用p1.then，不会去重新发起请求获取数据
答案
ABC CD
document.body.style.['background-color'] = '#fff'
document.body.style.setProperty('background-color', '#fff')
document.body.style = 'background-color': #fff'
document.body.style.fontSize = '14px'
A. event.cancelBubble = true;
B. event.stopPropagation();
C. event.preventDefault();
D. return false;
答案
BCD ABD
var x = typeof x
var res = typeof typeof x;
console.log(x, res)
var arr = [];
console.log(typeof arr, Object.prototype.toString.call(arr));
// case 1
function showCase(value) {
switch(value) {
case 'A':
console.log('Case A');
break;
case 'B':
console.log('Case B');
break;
case undefined:
console.log('Case undefined');
break;
default:
console.log('Case default');
}
}
showCase(new String('A'));
// case 2
function showCase(value) {
switch(value) {
case 'A':
console.log('Case A');
break;
case 'B':
console.log('Case B');
break;
case undefined:
console.log('Case undefined');
break;
default:
console.log('Case default');
}
}
showCase(String('A'));
<html>
<body>
<p id="demo"></p>
<script type="text/javascript">
var x = 10;
var y = "10";
document.getElementById("demo").innerHTML = Boolean(x == y);
</script>
</body>
</html>
function funcA(x){
var temp = 4;
function funcB(y){
document.write( ++x + y + (temp--));
}
funcB(5);
}
funcA(6)
var varArr = function(i,j,str) {
return j == 0 ? str : varArr(i,--j,(str+= " " + i[j]));
}
var arr = new Array('apple','orange','peach','lime');
var str = varArr(arr,arr.length,"");
alert(str);
function greetingMaker(greeting) {
function addName(name) {
greeting = greeting.split(' ').reverse().join("-");
return greeting + " " + name;
}
return addName;
}
var daytimeGreeting = greetingMaker("Good Day to you");
alert(daytimeGreeting(name));
String.prototype.GetNum = function() {
var regEx = /[^d]/g;
return this.replace(regEx, '');
};
var str = "a1b2c3";
str = str.GetNum();
alert(str);
function sum(a, b) {
return a + b;
}
sum(1, "2");
var str = "我非常喜欢编程";
str.length = 3;
console.log(str);
let number = 0;
console.log(number++);
console.log(++number);
console.log(number);
function nums(a, b) {
if (a > b)
console.log('a is bigger')
else
console.log('b is bigger')
return a + b
}
console.log(nums(4, 2))
console.log(nums(1, 2))
function side(arr) {
arr[0] = arr[2];
}
function func1(a, b, c = 3) {
c = 10;
side(arguments);
console.log(a + b + c);
}
function func2(a, b, c) {
c = 10;
side(arguments);
console.log(a + b + c);
}
func1(1, 1, 1);
func2(1, 1, 1);
var a = 3;
var b = new Number(3);
var c = 3;
console.log(a == b);
console.log(a === b);
console.log(b === c);
var a = [];
a.push(1, 2);
a.shift(3, 4);
a.concat([5, 6]);
a.splice(0, 1, 2);
var a = {}, b = '123', c = 123;
a[b] = 'b';
a[c] = 'c';
console.log(a[b]);
// example 2
var a = {}, b = Symbol('123'), c = Symbol('123');
a[b] = 'b';
a[c] = 'c';
console.log(a[b]);
// example 3
var a = {}, b = {key:'123'}, c = {key:'456'};
a[b] = 'b';
a[c] = 'c';
console.log(a[b]);
null == undefined
0.1 + 0.2 == 0.3
typeof NaN
typeof Function
typeof Object
typeof {}
'a' + 1
'a' - 1
Function instanceof Object
Object instanceof Function
var array = []
for(var i = 0; i < 3; i++) {
array.push(() => i)
}
var newArray = array.map(el => el())
console.log(newArray)
function a(m, n) {
var b = function (l) {
return l <= m ? l * b(l + 1) : 1;
}
return b(m - n + 1);
}
console.log(a(4, 2));
console.log(typeof undefined == typeof NULL);
console.log(typeof function () {} == typeof class {});
var a = 10
var b = {
age: 11
}
function fn(x,y) {
--y.age;
return --x;
}
fn(a,b)
var number = 4;
var numberFactorial = (function (number){
return (number === 0)? 1: number* factorial(number-1)
})(number)
console.log(numberFactorial)
var array = []
for(var i = 0; i < 3; i++) {
array.push(() => i)
}
var newArray = array.map(el => el())
console.log(newArray)
function addToList(item, list) {
return list.push(item)
}
const result = addToList("nowcoder", ["hello"])
console.log(result)
const first = () => { console.log('first'); return false; }
const second = () => { console.log('second'); return true; }
console.log( first() && second() );
console.log( second() || first() );
var s='12ab3cd', arr=s.split(/d/);
console.log(arr[3],arr[4])
function getAge(...args) {
console.log(typeof args);
}
getAge(21);
var arr=[1,2,3];
arr.push(arr.shift())
console.log(arr[1],arr[2])
题目解析：this指向题目解析及扩展[3]
关于this还可以看看：可能是最好的 this 解析了...
var x = 1;
var obj = {
x: 3,
fun:function () {
var x = 5;
return this.x;
}
};
var fun = obj.fun;
console.log( obj.fun(), fun() );
var a = 5;
function test() {
a = 0;
alert(a);
alert(this.a);
var a;
alert(a);
}
new test();
function fun () {
return () => {
return () => {
return () => {
console.log(this.name)
}
}
}
}
var f = fun.call({name: 'foo'})
var t1 = f.call({name: 'bar'})()()
var t2 = f().call({name: 'baz'})()
var t3 = f()().call({name: 'qux'})
let obj1 = {
a: 1,
foo: () => {
console.log(this.a)
}
}
// log1
obj1.foo()
const obj2 = obj1.foo
// log2
obj2()
const Person = (name="wang",age=10) => {
this.name = name;
this.age = age;
return this.name +' is '+ this.age + 'years old'
}
let result = new Person('zhang',11)
console.log(result)
var person = {
age: 18,
getAge: function() {
return this.age;
}
};
var getAge = person.getAge
getAge()
var name = 'global';
var obj = {
name: 'local',
foo: function(){
this.name = 'foo';
}.bind(window)
};
var bar = new obj.foo();
setTimeout(function() {
console.log(window.name);
}, 0);
console.log(bar.name);
var bar3 = bar2 = bar;
bar2.name = 'foo2';
console.log(bar3.name);
var obj = {
name:"zhangsan",
sayName:function(){
console.info(this.name);
}
}
var wfunc = obj.sayName;
obj.sayName();
wfunc();
var name = "lisi";
obj.sayName();
wfunc();
var name='test'
var a = {
name: 'ass',
getName: function() {
return this.name;
}
}
var b = a.getName;
b();
const promiseA = Promise.resolve('a')
promiseA. then((res) => {
console.log(res)
}).then((res) => {
console.log(res)
})
const promiseB = Promise.resolve('b')
promiseB. then((res) => {
console.log(res)
})
promiseB. then((res) => {
console.log(res)
})
setTimeout(() => {
console.log(1)
}, 0)
const P = new Promise((resolve, reject) => {
console.log(2)
setTimeout(() => {
resolve()
console.log(3)
}, 0)
})
P.then(() => {
console.log(4)
})
console.log(5)
setTimeout(function(){
console.log(1);
}, 0)
new Promise(function(resolve){
console.log(2);
resolve();
console.log(3);
}).then(function(){
console.log(4);
})
console.log(5);
(async () => {
console.log(1);
setTimeout(() => {
console.log(2);
}, 0);
await new Promise((resolve, reject) => {
console.log(3);
}).then(() => {
console.log(4);
});
console.log(5);
})();
new Promise((resolve) => {
console.log('1')
resolve()
console.log('2')
}).then(() => {
console.log('3')
})
setTimeout(() => {
console.log('4')
})
console.log('5')
var p1 = new Promise(function(resolve, reject){
resolve("2")
})
setTimeout(function(){
console.log("1")
},10)
p1.then(function(value){
console.log(value)
})
setTimeout(function(){
console.log("3")
},0)
setTimeout(function() {
console.log('setTimeout');
}, 0);
Promise.resolve().then(function() {
console.log('promise1');
}).then(function() {
console.log('promise2');
});
setTimeout(function() {
console.log(1)
},0)
new Promise(function executor(resolve){
console.log(2)
for (var i = 0; i<10000; i++) {
i - 9999 && resolve()
}
console.log(3)
}).then(function() {
console.log(4)
})
console.log(5)
<div class="outer">
<div class="inner"></div>
</div>
对应的js代码如下：
var outer = document.querySelector('.outer');
var inner = document.querySelector('.inner');
function onClick() {
console.log('click');
setTimeout(function() {
console.log('timeout');
}, 0);
Promise.resolve().then(function() {
console.log('promise');
});
outer.setAttribute('data-random', Math.random());
}
inner.addEventListener('click', onClick);
outer.addEventListener('click', onClick);
当点击class为inner的div块时，控制台依次输出结果是什么？ 10. 下面程序的输出结果是？
(async () => {
console.log(1);
setTimeout(() => {
console.log(2);
}, 0);
await new Promise((resolve, reject) => {
console.log(3);
}).then(() => {
console.log(4);
});
console.log(5);
})();
setTimeout(() => console.log('a'));
Promise.resolve().then(
() => console.log('b’);
).then(
() => Promise.resolve('c').then(
(data) => {
setTimeout(() => console.log('d'));
console.log('f');
return data;
}
)
).then(data => console.log(data));
console.log('one');
setTimeout(function() { console.log('two'); }, 0);
Promise.resolve()
.then(function() { console.log('three'); })
console.log('four');
setTimeout(function () {
console.log(C)
},0)
console.log('D')
new Promise(function(resolve){
console.log('E')
resolve()
console.log('F')
}).then(function() {
console.log('G')
})
console.log('H')
function log(msg, time) {
return new Promise((resolve) => {
setTimeout(() => {
console.log(msg);
resolve();
}, time);
});
}
则下面三段代码输出的结果是：
// 第一段代码：
(async () => {
for (let i = 0; i < 5; i++) {
await log(i, 1000);
}
})();
// 第二段代码：
(async () => {
[ 1, 2, 3, 4 ].forEach(async (i) => {
await log(i, 1000);
});
})();
// 第三段代码：
(async () => {
for (const i of [ 1, 2, 3, 4 ]) {
await log(i, 1000);
}
})();
关于原型JS：看完这篇文章，彻底了解 “原型” & “this”
传送门: 原型与原型链题目解析[4]
function Fn1(name) {
if(name){
this.name = name;
}
}
Fn1.prototype.name="jack"
let a = new Fn1();
console.log('a:', a.name);
function Fn2(name) {
this.name = name;
}
Fn2.prototype.name="jack"
let b = new Fn2();
console.log('b:', b.name);
var Foo = (function() {
var x = 0;
function Foo() {}
Foo.prototype.increment = function() {
++x;
console.log(x);
};
return Foo;
})();
var a = new Foo();
a.increment();
a.increment();
var b = new Foo();
a.increment();
var name = 'Jay'
function Person(name){
this.name = name;
console.log(this.name)
}
var a = Person('Tom')
console.log(name)
console.log(a)
var b = new Person('Michael')
console.log(b)
class A{}
class B extends A{}
const a = new A()
const b = new B()
a.__proto__
b.__proto__
B. __proto__
B. prototype.__proto__
b.__proto__.__proto__
function test() {
getName = function() {
Promise.resolve().then(() => console.log(0));
console.log(1);
};
return this;
}
test.getName = function() {
setTimeout(() => console.log(2), 0);
console.log(3);
};
test.prototype.getName = function() {
console.log(4);
};
var getName = function() {
console.log(5);
};
function getName() {
console.log(6);
}
test.getName();
getName();
test().getName();
getName();
new test.getName();
new test().getName();
new new test().getName();
var tmp = {};
var A = function() {};
A. prototype = tmp;
var a = new A();
A. prototype = {};
var b = Object.create(tmp);
b.constructor = A. constructor;
console.log(a instanceof A);
console.log(b instanceof A);
function Foo(){}
Foo.prototype.z = 3;
var obj = new Foo();
console.info(obj.z)
obj.z = 10;
console.info(obj.z);
delete obj.z;
console.info(obj.z);
const Book = {
price: 32
}
const book = Object.create(Book);
book.type = 'Math';
delete book.price;
delete book.type;
console.log(book.price);
console.log(book.type);
function sayHello() {
console.log(name);
console.log(age);
var name = "Tom";
let age = 18;
}
sayHello();
for (var i = 0; i < 3; i++) {
setTimeout(_ => {
console.log(i)
})
}
for (let i = 0; i < 3; i++) {
setTimeout(_ => {
console.log(i)
})
}
console.log(a);
var a = 'a';
console.log(b);
let b = 'b';
var foo = "Hello";
(function(){
var bar = " World";
alert(foo + bar);
})();
alert(foo + bar);
var a = 10;
(function () {
console.log(a)
a = 5
console.log(window.a)
var a = 20;
console.log(a)
})()
const a = 10
function runFunction() {
const a = 20
console.log('inside', a)
}
runFunction()
console.log('outside', a)
"use strict"
var name = 'Jay'
var person = {
name: 'Wang',
pro: {
name: 'Michael',
getName: function () {
return this.name
}
}
}
console.log(person.pro.getName)
var people = person.pro.getName
console.log(people())
<ul>
<li>1</li>
<li>2</li>
<li>3</li>
<li>4</li>
</ul>
<script>
var elements = document.getElementsByTagName("li");
for (var i=0;i<elements.length;i++){
elements[i].onclick =function( ){
alert(i);
};
}
compute(10,100);
var compute = function(A,B) {
console.info(A * B) ;
};
function compute(A,B){
console.info(A + B);
}
function compute(A,B){
console.info((A + B)*2);
}
compute(2,10);
meili()
function meili() {
console.log("meili")
}
mogu()
var mogu = function() {
console.log("mogu")
}
// 片段1
check('first');
function check(ars){
console.log(ars);
}
// 片段2
check('second');
var check= function(ars){
console.log(ars);
}
const student = {name: 'ZhangSan'}
Object.defineProperty(student, 'age', {value: 22})
console.log(student)
console.log(Object.keys(student))
function * cb(x, y) {
for(let i = Math.ceil(x); i <= y; i++) {
yield i;
}
}
var a = cb(6, 9);
console.log(a.next());
console.log(a.next());
function fn(...args) {
console.log(typeof args);
}
fn(21);
Promise.reject(0)
.catch(e => e)
.catch(e => console.log(e))
class Person {
constructor (name) {
this.name = name;
}
greet () {
console.log(`Hi, my name is ${this.name}`);
}
greetDelay (time) {
setTimeout(() => {
console.log(`Hi, my name is ${this.name}`);
}, time);
}
}
function getPersonInfo (one, two, three) {
console.log(one)
console.log(two)
console.log(three)
}
const person = 'Lydia'
const age = 21
getPersonInfo `${person} is ${age} years old`
// module.js
export default () => "Hello world"
export const name = "nowcoder"
// index.js
import * as data from "./module"
console.log(data)
// a.js
let a = 1
let b = {}
setTimeout(() => {
a = 2
b.b = 2
}, 100)
module.exports = { a, b }
// b.js
const a = require('./a')
console.log(a.a)
console.log(a.b)
setTimeout(() => {
console.log(a.a)
console.log(a.b)
}, 500)
<div id="box1">
<div id="box2">
content
</div>
</div>
<script>
const $ = document.querySelector.bind(document);
const box1 = $('#box1');
const box2 = $('#box2');
box1.addEventListener('click', () =>{
console.log('box1 true');
}, true);
box1.addEventListener('click', () =>{
console.log('box1 false');
}, false);
box2.addEventListener('click', () =>{
console.log('box2 true');
}, true);
box2.addEventListener('click', () =>{
console.log('box2 false');
}, false);
</script>
$(function () {
function fn1( value ) {
alert( value );
}
function fn2( value ) {
fn1("A");
return false;
}
var callbacks = $.Callbacks();
callbacks.add( fn1 );
callbacks.fire( "B" );
callbacks.add( fn2 );
callbacks.fire( "C" );
})
<html>
<head>
<script type="text/javascript" src="/jquery/jquery.js"></script>
<script type="text/javascript">
$(document).ready(function(){
$("button").click(function(){
$("<b>Hello World!</b>").______("p");
});
});
</script>
</head>
<body>
<p>This is a paragraph.</p>
<p>This is another paragraph.</p>
<button>在每个p元素的结尾添加内容</button>
</body>
</html>
<div id="box1">
<div id="box2">
content
</div>
</div>
<script>
const $ = document.querySelector.bind(document);
const box1 = $('#box1');
const box2 = $('#box2');
box1.addEventListener('click', () => {
console.log('box1 true');
}, true);
box1.addEventListener('click', () => {
console.log('box1 false');
}, false);
box2.addEventListener('click', () => {
console.log('box2 true');
}, true);
box2.addEventListener('click', () => {
console.log('box2 false');
}, false);
</script>
var vm = new Vue({
el: '#example',
data: {
message: 'Hello'
},
computed: {
test: function () {
console.log(1)
return this.message
}
},
created: function (){
this.message = 'World'
for (var i = 0; i < 5; i++) {
console.log(this.test)
}
}
})
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