javascript Array Cardio

Posted 2021-05-04

const users = [
    {
        id: 1,
        name: 'Allison',
        age: 4,
        gender: 'female'
    },
    {
        id: 2,
        name: 'Derek',
        age: 1,
        gender: 'male'
    },
    {
        id: 3,
        name: 'Irene',
        age: 35,
        gender: 'female'
    },
    {
        id: 4,
        name: 'Danny',
        age: 32,
        gender: 'male'
    },
    {
        id: 5,
        name: 'Alin',
        age: 25,
        gender: 'female'
    },
]

// console.log('users', users)

// 1. forEach log each name

// users.forEach((user) => {
//     console.log(user.name)
// })

// 2. forEach 把每個user age 乘 2

// users.forEach((user, index) => {
//     return users[index].age = user.age * 2
// })
// console.log('users', users)

// map
// 3. log username

// users.map(user => console.log(user.name))

// 4.  把每個user age 乘 2

// let doubled = users.map((user) => {
//     let tempObj = {}
//     tempObj = {...user}
//     tempObj.age = user.age * 2
//     return tempObj
// })

// console.log('doubled', doubled)
// console.log('users', users)
// map won't change original array
// foreach will change original array

// Filter
// 5. 只要 age 低於 18

// let kids = users.filter((user) => {
//     let tempObj = {}
//     tempObj = {...user}
//     return tempObj.age < 18
// })

// 6. Only female
// let female = users.filter((user) => {
//     let tempObj = {}
//     tempObj = {...user}
//     return tempObj.gender === 'female'
// })

// console.log('female', female)


// Reduce
// 6. 把所有users 的年齡加起來

let totalAge = users.reduce((acc, obj) => {
    return acc + obj.age
}, 0)

// 0 + 4 = 4
// 4 + 1 = 5
// 5 + 35 = 40
console.log(totalAge)