面试中的作用域题和THIS 指向的问题

作用域的面试题

1.

fn()

function fn () {

console.log(12)

}

var as = function () {

console.log(45)

}

2.

var a = 12;

function fn () {

console.log(a)

var a = 45;

console.log(a)

}

fn()

3.

var a = 12;

function fn () {

console.log(a)

a = 45;

console.log(a)

}

fn()

4.

function fn () {

console.log(11)

function ff () {

console.log(22)

}

ff()

}

fn()

5.

function fn () {

console.log(5)

fn()

}

fn()

6.

function fn () {

console.log(12)

}

var as = fn()

console.log(as)

7.

function fn () {

console.log(12);

return 45;

console.log(456)

}

var as = fn()

8.

var a = 12;

function fn () {

console.log(a);

return 4;

var a = 45;

}

fn()

9.

var a = 45;

function fn () {

console.log(a)

}

fn()

10.

var a = 45;

function fn (a) {

console.log(a)

}

fn(5)

11.

var a = 123;

function fun () {

alert(a);

}

fun()

12.

var a = 123;

function fun () {

alert(a);

var a = 456;

}

fun();

alert(a);

13.

var a = 123;

function fun () {

alert(a);

a = 456;

}

fun()

alert(a)

14.

var a = 123;

function fun (a) {

alert(a)

a = 456;

}

fun()

alert(a)

15.

var a = 123;

function fun (a) {

alert(a)

a = 456

}

fun()

alert(a)

 

16.

function makeNoSense (x) {

this.x = x;

}

makeNoSense(5);

console.log(x);

function test () {

this.x = 1;

alert(this.x);

}

test();

 

 

This

1.

var name = '222';

var a = {

name : '111',

say : function () {

console.log(this.name)

}

}

var fun = a.say;

fun() //???

a.say() //???

var b = {

name : '333',

say : function (fun) {

fun();

}

}

b.say(a.say); //???

b.say = a.say;

b.say() //???

 

2.

var val = 1
var obj = {
val : 2,
dbl : function() {
var val = 45;
console.log(this); //指向谁？
this.val *= 2;
console.log(this.val); //？？
console.log(val); //？？
}
}
var fn = obj.dbl
fn()

3.

var x = 12;
function test() {
console.log(this.x)
}
test() //??

4.

var x = 12;
function test() {
console.log(this.x)
}
var obj={
x:45,
ss:test
}
obj.ss() //??

5.

var x = 12;
function test() {
console.log(this.x)
}
var obj = {
x:45,
ss:function(){
console.log(this)
test()
}
}
obj.ss() //??

6.

var val = 1
var obj = {
val : 2,
dbl : function() {
// var val = 45;
console.log(this); // 指向谁
this.val *= 2;
console.log(this.val); // ???
console.log(val); // ???
}
}
var ff = obj.dbl()