Displaying Syntax Error

Tell us what’s happening:
SyntaxError: unknown: Legacy octal literals are not allowed in strict mode (8:5)

6 |
7 | a += 12;

8 | b += 09;
| ^
9 | c += 7;

Your code so far


var a = 3;
var b = 17;
var c = 12;

// Only modify code below this line

a += 12;
b += 09;
c += 7;

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/79.0.3945.130 Safari/537.36.

Challenge: Compound Assignment With Augmented Addition

Link to the challenge:
https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/basic-javascript/compound-assignment-with-augmented-addition

it is not liking you wrote 09 instead of 9

Thanks a lot!
So why is it not working?

Because 09 is interpreted as a number in base eight because of the 0 in front of 9 yet a number in base eight cannot have the digit 9 but only the digits 0,1,2,3,4,5,6,7. And in strict mode as stated in the error message, octal literals are not allowed. Read more here about strict mode in JS