Why (Uncaught TypeError: $div1.offset is not a function)?

Question

Hello guys,
I want create a 2D car game, where dogde obstacles that arrive from the top.
In my program -> https://code.sololearn.com/Wxann6l3d3tJ/#js
in JS, the function collision() doesn't work. The console return " Uncaught TypeError: $div1.offset is not a function Line:11. Why? What is it? Thank you

Answer 1

dx_button and sx_button variables doesn't exist
Line 36

Answer 2

OMG ahahaha you taught me a very useful basic! Thank you very much :)