Four JavaScript face test your JS basic skills

There are four short JavaScript scripts below, and if you can predict the results of your script, your JavaScript skills will be fine. If the answer is wrong, you can fill out the missing knowledge accordingly. Anyway is very simple, the wrong answer just means you do not understand it, look at the information will soon understand. Then do it first, to see the answer please click the RunCode button. Dancheng Shu Marine Environmental protection

First question

1	vara = 10;

2

sayHi();

3	functionsayHi() {

4	vara = 20;

5

alert(a);

6

}

7

alert(a);

Second question

1	vara = 10;

2

sayHi();

3	functionsayHi() {

4

a = 20;

5

alert(a);

6

}

7

alert(a);

Third question

01	vara = 10;

02

sayHi();

03	functionsayHi()

04

{

05	a = a + 10;

06

alert(a);

07

returna;

08

}

09

alert(a);

10	alert(sayHi()+10);

Question Fourth

01	vara = 10;

02

sayHi();

03	functionsayHi()

04

{

05	vara = a + 10;

06

alert(a);

07

returna;

08

}

09

alert(a);

10	alert(sayHi()+10);

Four JavaScript face test your JS basic skills