How to make the search value change via javascript?

[choi12191995]

I use the input type to make a live search.
But I need to have a function that auto input the value into the live search input element.
I try to write the code in console: $("#querySearch").val("test");
it didnt cahnge the value on the input element, but check by $("#querySearch").val(), it return "test"

I also set the code, $("#querySearch").val("test")on document reday and onload function, it output same result.

But I set this code inside an onclick function, the input element can display "test" immediately.