JavaScript 判断变量是否为空---三元运算,元组获取值-重组.map()。

var from_days = getQueryString('from_days');
undefined
{'from_days': (from_days) ? from_days : null}
{from_days: null}
var from_hours = getQueryString('from_hours')
undefined
{'from_days': (from_hours) ? from_hours : null}
{from_days: "1"}

cpu_data =  [['11:02:42', 12.3], ['11:02:47', 11.4], ['11:02:52', 13.3], ['11:02:57', 9.5], ['11:03:02', 12.6], ['11:03:07', 9.2]]
(6) [Array(2), Array(2), Array(2), Array(2), Array(2), Array(2)]
time_list = cpu_data.map(item =>item[0])
(6) ["11:02:42", "11:02:47", "11:02:52", "11:02:57", "11:03:02", "11:03:07"]

.map() 应用https://www.jb51.net/article/150818.htm

 变量赋值时的三元运算写法

        var host = window.location.host;　　//127.0.0.1
        var proto = window.location.protocol;
        var ws_proto = (proto === "http:" ? "ws:" : "wss:");