Insert text at cursor position

gistfile1.js

function insertAtCursor(myField, myValue) {
	if(document.selection){
		myField.focus();
		sel = document.selection.createRange();
		sel.text = myValue;
	} else if(myField.selectionStart || myField.selectionStart == '0') {
		var startPos = myField.selectionStart;
		var endPos = myField.selectionEnd;
		myField.value = myField.value.substring(0, startPos) + myValue + myField.value.substring(endPos, myField.value.length);
	} else {
		myField.value += myValue;
	}
}

insertAtCursor(document.getElementById('myFieldId'), 'test');