Someone told me that there's !< and !> in JavaScript. I tried it but it didn't work. Is there something like this in JavaScript? If not in JavaScript, is it there in any other language?
No. In JavaScript and many other languages (for numbers - not NaN - and strings):
"!<" is >=
"!>" is <=
Check this: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Comparison_Operators