1.函数声明和函数表达式有什么区别
使用function关键字可以声明一个函数(声明不必放到调用的前面)
<p>//函数调用
sayHello()
//函数声明
function sayHello(){
console.log("hello")
}</p>
函数表达式(声明必须放到调用的前面),不然就是输出undefined
var sayHello = function(){
console.log("hello");
}
sayHello()
2.什么是变量的声明前置？什么是函数的声明前置
Paste_Image.png
3.arguments 是什么
类数组对象，可以使用arguments来获得函数的所有传入参数
function ptintInfo(name,age,sex){
console.log(name);
console.log(age);
console.log(sex);
console.log(arguments[0])
console.log(arguments[1])
console.log(arguments[2])
}
printInfo('Eric',28,'male')
4.函数的"重载"怎样实现
function printPeopleInfo(name,age,sex){
if(name){
console.log(name);
}
if(age){
console.log(age);
}
if(sex){
console.log(sex);
}
}
printPeopleInfo('Byron',26);
printPeopleInfo('Byron',26,'male');
通过不同的参数调用执行相应的逻辑
5.立即执行函数表达式是什么？有什么作用
(function fn1() {})();
(function fn2() {})；//括号
[function fn3() {}];//数组
1,function fn4() {};//逗号
隔离作用域
6.求n!，用递归来实现
function factor(n) {
if (n === 1){
return 1 ;
}
return factor (n-1)*n
}
for循环
function factor(n) {
var result = 1;
for (var i = 0,i<n,i++){
result=result*i
}
}
7.
function getInfo(name, age, sex){
console.log('name:',name);
console.log('age:', age);
console.log('sex:', sex);
console.log(arguments);
arguments[0] = 'valley';
console.log('name', name);
}
getInfo('饥人谷'，2，'男')
//name:饥人谷 age:2 sex:男 ['饥人谷'，2，'男'] name vally
getInfo('小谷'，3)
//name:小谷 age:3 sex:undefined ['小谷'，3] name vally
getInfo('男')
//name:undefined age:undefined sex:男 ['男'] name vally
8
function sumOfSquares(a,b,c){
if(a){
a=a*a;
}
else{
a=0;
}
if(b){
b=b*b;
}
else{
b=0;
}
if(c){
c=c*c;
}
else{
c=0;
}
console.log(a+b+c);
}
var result = sumOfSquares(3)
console.log(result)//9
var result = sumOfSquares(2,3,4)
console.log(result) //29
var result= sumOfSquares(1,3)
console.log(result) //10
9
console.log(a)
var a=1
console.log(b)
等价于
var a
console.log(a)
//undefined;var a声明前置，但未被赋值
a=1
console.log(b)
//报错；前面b没有被赋值
10
sayName('world');
sayAge(10);
function sayName(name){
console.log('hello ', name);
}
var sayAge = function(age){
console.log(age);
};
//hello world ,报错；sayName是一个function声明的函数，不需要前置；sayAge是var声明的一个函数，需要前置
11
var x = 10
bar()
function foo() {
console.log(x)
}
function bar(){
var x = 30
foo()
}
//10;
//1.globalContext={
AO:{
x=10
foo:function
bar:function},
Scope: null
}
2.barContext={
AO:{
x=30;
},
scope:bar.[[scope]]=globalContext.AO
3.fooContext={
AO:{},
Scope:foo.[[scope]]=globalContext.AO
}//调用foo的时候找到globalContext.AO里面x=10，输出10
12
var x = 10;
bar()
function bar(){
var x = 30;
function foo(){
console.log(x)
}
foo();
}
//1.globalContext={
AO:{
x=10
bar:function},
Scope: null
}
bar.[[scope]]=globalScope.AO
2.barContext={
AO:{
x=30;
foo:function
},
scope:bar.[[scope]]=globalContext.AO
3.fooContext={
AO:{},
Scope:foo.[[scope]]=barContext.AO
}//foo()找到barContext.AO中x=30，输出30
13
var x = 10;
bar()
function bar(){
var x = 30;
(function (){
console.log(x)
})()
}
//30;
//1.globalContext={
AO:{
x=10
bar:function},
Scope: null
}
bar.[[scope]]=globalScope.AO
2.barContext={
AO:{
x=30;
},
scope:bar.[[scope]]=globalContext.AO
//查找到x=30
14
var a = 1;
function fn(){
console.log(a)
var a = 5
console.log(a)
a++
var a
fn3()
fn2()
console.log(a)
function fn2(){
console.log(a)
a = 20
}
}
function fn3(){
console.log(a)
a = 200
}
fn()
console.log(a)
//undefined,5,1,6,20,200
//1.globalContext={
AO:{
a=1
fn:function
fn3:function},
Scope: null
}
fn.[[scope]]=globalContext.AO
fn3.[[scope]]=globalContext.AO
2.fnContext={
AO:{
a//输出undefined------Ⅰ
a=5//输出5------Ⅱ
//fn3()在globalContext.AO中找到a=1，*(这时候globalContext中a=200)*输出1-----Ⅲ
//fn2()，a++后a=6，*(这时候fnContext.AO中a=20)*输出6-----Ⅳ
//console.log(a);输出20-----Ⅴ
fn2:function
},
scope:fn.[[scope]]=globalContext.AO
3.fn3Context={
AO:{}
Scope.fn3[[scope]]=globalContext.AO
4.fn2Context={
AO:{}
Scope.fn2[[scope]]=fnContext.AO
//console.log(a)输出globalContext.AO中a=200-----Ⅵ
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