动态显示输入框placeholder文字

html

<input type="text" name="" id="jgChatInput" class="duihIntI" />

js

<script>
    /*输入框依次显示文字*/
    var userIput = document.querySelector(".duihIntI");
    var i = 0;
    var s = "在此输入问题可直接对话";
    var clock = setInterval(function() {
        i++;
        if(i > 12) {
            i = 0;
        }
        var p = s.slice(0, i);
        userIput.setAttribute("placeholder", p);
    }, 600)
    userIput.addEventListener("focus", function() {
        clearInterval(clock)
        userIput.setAttribute("placeholder", "")
    })
    /*依次显示文字结束*/
</script>