dom中的隐藏和读取

var a = document.getElementById('showLeft');

var btn = document.getElementById('btn');

function tn() {

if(btn.innerHTML=="<<") {

a.style.display = 'none';

document.getElementById('btn').innerHTML = ">>"

} else {

a.style.display = 'block';

document.getElementById('btn').innerHTML = "<<"

}

}