Cursor position in textarea on insert

I am working on a little emoji function. My problem is when I have a text in the textarea and select an emoji from the drop down the emoji always goes to the end of the text even if I place the cursor at the beginning of the text, the emoji will go to the end of the text like so:

Some text here View attachment 243231

The code:

function insertSmiley(smiley)
{
var currentText = document.getElementById("textarea");
var smileyWithPadding =" "+ smiley +" ";
currentText.value +=...

Code (markup):

Cursor position in textarea on insert

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