why does several javascript libraries use $ for one or other use

Question

I have seen several javascript libraries using $ be it jQuery , mootools , prototype etc also even some of the books on javascript recommend using $ as a function replacement of document.getElementById. is it just a random thing.

Answer 1

The reason $ was actually introduced as a valid variable name in the ECMA specs was to distinguish machine generated code from human written code .
Most JS libraries use $ because it is very rare that you would want to name some of your variable $ and hence it would avoid collision and accidental overwriting of the variable . ( However now since every library is using $ , if you want to use two libraries , you are in a soup ) .