js：Array.reduce累加计算、合并数组

array.reduce(function(prevValue, currentValue, currentIndex, arr), initialValue)

let list = [1, 2, 3, 5];
let result = list.reduce((prevValue, currentValue)=>{
  return prevValue + currentValue;
}, 0);
console.log(result);
// 11

let list = [[1, 2, 3], [], [8, 9]];
let result = list.reduce((prevArr, currentArr)=>{
  return prevArr.concat(currentArr);
}, []);
console.log(result);
// [ 1, 2, 3, 8, 9 ]