How to make the search value change via javascript?

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.