javascript - 什么时候使用reduce和reduceRight？

Question

你能为我描述一下吗？

var arr, total;
arr = [1, 2, 3, 4, 5];
total = arr.reduce(function(previous, current) {
return previous + current;
});
// total is 15

Answer 1

reduce的顺序是从左到右，reduceRight的顺序是从右到左，如下代码所示:

var arr = ["1", "2", "3", "4", "5"];

total1 = arr.reduce(function(prev, cur) {
    return prev + cur;
});

total2 = arr.reduceRight(function(prev, cur) {
    return prev + cur;
});

console.log(total1); // => 12345
console.log(total2); // => 54321