数组筛选和排序

涉及JavaScript基本语法、事件、DOM相关的知识。

<h3>污染城市列表</h3>
    <ul id="aqi-list">
    </ul>

    <script type="text/javascript">
        var aqiData = [
            ["北京", 90],
            ["上海", 50],
            ["福州", 10],
            ["广州", 50],
            ["成都", 90],
            ["西安", 100],
            ["长沙", 88],
        ];

        (function() {
            /*
            在注释下方编写代码
            遍历读取aqiData中各个城市的数据
            将空气质量指数大于60的城市显示到aqi-list的列表中
            */
            //筛选符合条件的数组并构成新的数组newArr
            var newArr = [];
            for (var i = 0, j = aqiData.length; i < j; i++) {
                if (aqiData[i][1] > 60) { //数组 var aqiData = [ ["北京", 90]]中要取90用：aqiData[i][1]
                    newArr.push([aqiData[i][0], aqiData[i][1]]);
                }
            }
            // 数组大到小排序
            newArr.sort(function(a, b) {
                return b[1] - a[1];
            })
            var all = "";
            for (var i = 0, j = newArr.length; i < j; i++) {
                //名次中文化
                var rank = i + 1
                switch (rank) {
                    case 1:
                        rank_number = "一";
                        break;
                    case 2:
                        rank_number = "二";
                        break;
                    case 3:
                        rank_number = "三";
                        break;
                    default:
                        rank_number = "前三以外忽略不计";
                        break;
                }
                //添加文本
                all += "<li>第" + rank_number + "名" + ":" + newArr[i][0] + " " + newArr[i][1] + "</li>";
                var ul = document.getElementById('aqi-list');
                ul.innerHTML = all;
            }
        })();
    </script>

关于升序排列和降序排列

var test = [6, 2, 10];
test.sort(function(a, b) {
    return a - b;         //联想负数在前，正数在后，前减后升序、后减前降序
});
console.log(test); //[2, 6, 10]