解决 IE8 不支持console

window.console = window.console || (function () {
    var c = {}; c.log = c.warn = c.debug = c.info = c.error = c.time = c.dir = c.profile= c.clear = c.exception = c.trace = c.assert = function () { };
    return c;
})();

//放在<script></script>的下面第一行