Add a text inside multiline input, without reset initial content

Need help
16

I suspect it is easy enough with a little Javascript.

image

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function insertAtCaret(areaId, text) {
		var txtarea = document.getElementById(areaId);
		if (!txtarea) { return; }

		var scrollPos = txtarea.scrollTop;
		var strPos = 0;
		var br = ((txtarea.selectionStart || txtarea.selectionStart == '0') ?
			"ff" : (document.selection ? "ie" : false ) );
		if (br == "ie") {
			txtarea.focus();
			var range = document.selection.createRange();
			range.moveStart ('character', -txtarea.value.length);
			strPos = range.text.length;
		} else if (br == "ff") {
			strPos = txtarea.selectionStart;
		}

		var front = (txtarea.value).substring(0, strPos);
		var back = (txtarea.value).substring(strPos, txtarea.value.length);
		txtarea.value = front + text + back;
		strPos = strPos + text.length;
		if (br == "ie") {
			txtarea.focus();
			var ieRange = document.selection.createRange();
			ieRange.moveStart ('character', -txtarea.value.length);
			ieRange.moveStart ('character', strPos);
			ieRange.moveEnd ('character', 0);
			ieRange.select();
		} else if (br == "ff") {
			txtarea.selectionStart = strPos;
			txtarea.selectionEnd = strPos;
			txtarea.focus();
		}

		txtarea.scrollTop = scrollPos;
	}

insertAtCaret('myField', "foo");