求和：一共走了多少路
var trips = [
{ distance: 34 },
{ distance: 12 },
{ distance: 1 }
]
var totalDistance;
totalDistance = trips.reduce((sum,trip) => sum += trip.distance,0)
统计：有多少站着的多少坐着的
var desks = [
{ type: 'sitting' },
{ type: 'standing' },
{ type: 'sitting' },
{ type: 'sitting' },
{ type: 'standing' }
]
var deskTypes = desks.reduce(function(r,desk) {
if(desk.type === 'sitting') {
r.sitting +=1
return r
}
if(desk.type === 'standing') {
r.standing +=1
return r
}
}, { sitting: 0, standing: 0 })
使用reduce实现unique：输入[1,1,2,2,1,4,3]，返回[1,2,4,3]
function unique(array) {
return array.reduce((uniq,e) => {
if(!uniq.includes(e)){
uniq.push(e)
return uniq
}
return uniq
},[])
}
