JS实现的插入样式的方法

JS实现的插入样式的方法，摘抄自citypick插件

var styleInject = function (css, elem) {
    if (!css || typeof document === 'undefined') {
        return;
    }

    var head = elem ? elem : document.getElementsByTagName('head')[0];
    var style = document.createElement('style');
    style.type = 'text/css';

    if (head.firstChild) {
        head.insertBefore(style, head.firstChild);
    } else {
        head.appendChild(style);
    }

    if (style.styleSheet) {
        style.styleSheet.cssText = css;
    } else {
        style.appendChild(document.createTextNode(css));
    }
};
var css = '.city-picker-input{opacity:0 !important;top:-9999px;left:-9999px;position:absolute;}.city-picker-span{position:relative;display:block;outline:0;-webkit-tap-highlight-color:rgba(0,0,0,0);border-bottom:1px solid #ccc;background-color:#fff;color:#ccc;cursor:pointer;}.city-picker-span > .placeholder{color:#aaa;}.city-picker-span > .arrow{position:absolute;top:50%;right:8px;width:10px;margin-top:-3px;height:5px;background:url(/static/plugs/city-picker/images/drop-arrow.png) -10px -25px no-repeat;}.city-picker-span.focus,.city-picker-span.open{border-bottom-color:#46A4FF;}.city-picker-span.open > .arrow{background-position:-10px -10px;}.city-picker-span > .title > span{color:#333;padding:5px;border-radius:3px;}.city-picker-span > .title > span:hover{background-color:#f1f8ff;}.city-picker-dropdown{position:absolute;width:315px;left:-9999px;top:-9999px;outline:0;-webkit-tap-highlight-color:rgba(0,0,0,0);z-index:999999;display:none;min-width:330px;margin-bottom:20px;}.city-select-wrap{box-shadow:0 1px 5px rgba(0,0,0,0.5);}.city-select-tab{border-bottom:1px solid #ccc;background:#f0f0f0;font-size:13px;}.city-select-tab > a{display:inline-block;padding:8px 22px;border-left:1px solid #ccc;border-bottom:1px solid transparent;color:#4D4D4D;text-align:center;outline:0;text-decoration:none;cursor:pointer;font-size:14px;margin-bottom:-1px;}.city-select-tab > a.active{background:#fff;border-bottom:1px solid #fff;color:#46A4FF;}.city-select-tab > a:first-child{border-left:none;}.city-select-tab > a:last-child.active{border-right:1px solid #ccc;}.city-select-content{width:100%;min-height:10px;background-color:#fff;padding:10px 15px;box-sizing:border-box;}.city-select{font-size:13px;}.city-select dl{line-height:2;clear:both;padding:3px 0;margin:0;}.city-select dt{position:absolute;width:2.5em;font-weight:500;text-align:right;line-height:2;}.city-select dd{margin-left:0;line-height:2;}.city-select.province dd{margin-left:3em;}.city-select a{display:inline-block;padding:0 10px;outline:0;text-decoration:none;white-space:nowrap;margin-right:2px;color:#333;cursor:pointer;}.city-select a:hover,.city-select a:focus{background-color:#f1f8ff;border-radius:2px;color:#46A4FF;}.city-select a.active{background-color:#46A4FF;color:#fff;border-radius:2px;}';
styleInject(css);