Special Case: Unable to insert text in textarea on cursor position in Browser using JavaScript

I want to insert text in Instagram Chat textarea using javascript

Instagram textarea(in messages tab) can be accessed by using….

const textArea = document.getElementsByClassName("_ab5y")[0].getElementsByClassName("_acrb")[0].children[1].getElementsByTagName("textarea")[0];

the value can be inserted easily using…

    function setKeywordText(text) {
        textArea.value = text;
        var evt = document.createEvent("Events");
        evt.initEvent("input", true, true);
        textArea.dispatchEvent(evt);
    }

    setKeywordText("Hello!");

But, Unable to Insert text on cursor position.

Note-
1. I know that initEvent is deprecated. But alternative is NOT working.
2. I don’t want to change value (like- append text as string and then, change whole to the textarea).

Is there any way to do this?

>Solution :

Tested on Instagram, this code can insert text in the cursor position.

const textArea = document.getElementsByClassName("_ab5y")[0].getElementsByClassName("_acrb")[0].children[1].getElementsByTagName("textarea")[0];

function setKeywordText(text) {
  const startPos = textArea.selectionStart;
  const endPos = textArea.selectionEnd;
  const messageStart = textArea.value.substring(0, startPos);
  const messageEnd = textArea.value.substring(endPos, textArea.value.length);
  textArea.value = messageStart + text + messageEnd;
  textArea.setSelectionRange(startPos + text.length, startPos + text.length);
}

setKeywordText("Hello!");