Please try to describe your issue in more detail in the ‘tell us what is happening’ section in future, you can write your own text in this section. It makes helping much easier.
Now, look at this bit of your code.
var ab;
You declared a new variable, ab. Read the instructions carefully, does the example code or lesson say to declare a new variable?
Note that your code can pass without changing this, but that extra code may not be doing what you think it is.