Four JavaScript interview questions to test your basic js skills

There are four short JavaScript scripts below. If you can successfully predict the running results of the script, your basic JavaScript skills are still acceptable. If the answer is incorrect, you can add missing knowledge accordingly. It is also very simple. If you get a wrong answer, it means you don't understand it. You will soon understand the information. Click the runcode button to see the answer first.

Question 1

var a = 10;sayHi();function sayHi() {var a = 20;alert(a);}alert(a);

Question 2

var a = 10;sayHi();function sayHi() {a = 20;alert(a);}alert(a);

Question 3

var a = 10;sayHi();function sayHi(){a = a + 10;alert(a);return a;}alert(a);alert(sayHi()+10);

Question 4

var a = 10;sayHi();function sayHi(){var a = a + 10;alert(a);return a;}alert(a);alert(sayHi()+10);