2-2Date-获取年月日时分秒练习4-4Math-random练习4-3Math-round练习4-2Math-floor练习4-1Math-ceil练习3-4Array-二维数组平均分练习3-3Array-数组打印星星练习3-2Array-属性和方法练习3-1Array-数组练习1-1String-length练习2-1Data-获取当前时分秒练习1-7String-toUpperCase练习1-6String-toLowerCase练习1-5String-split练习1-4String-substring练习1-3String-indexOf练习1-2String-charAt练习