Javascript, avoid cursor moving at textbox end

I have a js funciton executed at one textbox OnKeyUp event.

The textbox has a valu开发者_如何学Ce by default.

If I place my cursor in the middle of the string and I add a char, the cursor moves at the end of the string.

I know that this is because the executed function recalculate and set the textbox value.

Is there a way to avoid the cursor moving at the end of the string?

Thanks

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Changing the value of the text in the textbox will always move the cursor to the end