(1) Reducir la sintaxis
array.reduce(function(total, currentValue, currentIndex, arr), initialValue)
reduce recibe dos parámetros
ejemplo:
let arr = [1, 2, 3, 4, 5]
// 下标是奇数的元素和
var result = arr.reduce((total, item, index) => {
total += (index % 2 ? item : 0)
return total
}, 0)
console.log(result) // 6
El valor inicial es 0
(2) Escriba reducir a mano a continuación
Array.prototype.reduce = function (callback, initValue) {
let result = initValue // result 赋值 为传过来的初始值
for (var index = 0; index < this.length; index++) {
result = callback(result, this[index], index, this) // 循环重新计算 result
}
return result // 返回result
}
transferir:
Array.prototype.reduce = function (callback, initValue) {
let result = initValue
for (var index = 0; index < this.length; index++) {
result = callback(result, this[index], index, this)
}
return result
}
// 下标是奇数的元素和
let arr = [1, 2, 3, 4, 5]
var res = arr.reduce((total, item, index) => {
total += (index % 2 ? item : 0)
return total
}, 0)
console.log(res) // 6