reduce定义遍历数组中的每一项，并在被函数处理后，将其结果汇总为单个返回值语法arr.reduce(function(total,current,currentIndex,arr),initialValue)typescript方法定义reduce(callbackfn:(previousValue:T,currentValue:T,currentIndex:number,array:T[])=>T):T);reduce(callbackfn:(previousValue:T,currentValue:T,currentIndex:number,array:T[])=>T,initialValue:T):T;reduce(callbackfn:(previousValue:U,currentValue:T,currentIndex:number,array:T[])=>U,initialValue:U):U;过滤掉满足条件的case，存入数组constarr=[{value:10},{value:11},{value:12}]constarr2=arr.reduce((temp,item)=>{if(item.value>10){temp.push(item.value);}returntemp},[])arraysumletarr=[{value:10},{value:11},{value:12}]letmean=arr.reduce((temp,item,index)=>{returntemp+item;})使用reduce求平均值，一步letmean=arr.reduce((temp,item,index)=>{如果（索引
