//设定选中范围
someInput.setSelectionRange(0, 2);

//只读
<input type="text" value="2" readonly />

//绑定键盘输入事件
someInput.addEventListener('keydown', function (event) {
　　//......
});

//获取光标位置

<input type="text" id="text-element" />

<!-- Or a textarea

<textarea id="text-element"></textarea>

-->

<input type="button" id="trigger" value="Check"/>

<script>

    document.getElementById("trigger").addEventListener("click", function(){

        var myElement = document.getElementById('text-element');

        var startPosition = myElement.selectionStart;

        var endPosition = myElement.selectionEnd;

        // Check if you've selected text

        if(startPosition == endPosition){

            alert("The position of the cursor is (" + startPosition + "/" + myElement.value.length + ")");

        }else{

            alert("Selected text from ("+ startPosition +" to "+ endPosition + " of " + myElement.value.length + ")");

        }

    },false);

</script>