Array.reduce() 数组内置方法

reduce的意思是“把...数量、程度或大小上变小”。
对于Array.reduce()来说，就是把数组元素通过特定的逻辑(callback)转成更小的数组或某一特定的类型。
正因如此，它非常的灵活，功能也非常的强大，是其他数组内置方法所不能比拟的

在使用reduce()方法的时候，对于非确定元素个数的数组，始终加个initVal会更加的保险

const numbers = [1,2,3]
const summation = numbers.reduce(
    (accumulator, curVal) => accumulator + curVal,
    0
)
console.log(summation )  //6

实战使用-数组转数字

const salary = 30000;

const consumption = [
    {cost: 6000, type:'a'},
    {cost: 2000, type:'b'},
    {cost: 3000, type:'c'},
    {cost: 4000, type:'d'},
]

const balance = consumption.reduce((accumulator,curVal) => accumulator - curVal.cost,salary)
console.log('balance:',balance); // balance: 150000

实战使用-对象转数组

const ageGroup = [18,21,1,1,41,14,4,13,14,5,10]

const uniqueAgeGroup = ageGroup.reduce((accumulator,currentValue) => {
if(!accumulator.includes(currentValue)){
    accumulator.push(currentValue);
}
return accumulator
},[])

console.log('uniqueAgeGroup:',uniqueAgeGroup); // uniqueAgeGroup: (9) [18, 21, 1, 41, 14, 4, 13, 5, 10]

实战使用-数组转对象

const people = [
{name: 'John',age: 23},
{name: 'Orage',age: 18},
{name: 'Pink',age: 25},
{name: 'Redux',age: 56},
{name: 'Kerwin',age: 25},
{name: 'Ww',age: 18},
{name: 'Fincus',age: 56},
]

const groupBy = (objectArray,property) => {
return objectArray.reduce((accumulator,currentObject) => {
    const key = currentObject[property];
        if(!accumulator[key]){
        accumulator[key] = []
        }
        accumulator[key].push(currentObject);
        return accumulator
},{})
}

const groupPeople = groupBy(people,'age');
console.log('groupPeople:',groupPeople);
//{
　　18: (2) [{name: 'Orage', age: 18}, {name: 'Ww', age: 18}]
　　23：[{name: 'John', age: 23}]
　　25: (2) [{name: 'Pink', age: 25}, {name: 'Kerwin', age: 25}]
　　56: (2) [{name: 'Redux', age: 56}, {name: 'Fincus', age: 56}]
}