number陣列 求和

const arr = [1,2,3,5,6]
const summary = arr.reduce((pre,cur,index,array)=>{ return x = pre + cur },0)  // summary : 17

物件陣列指定項 求和

const arr = [{name:"lisi",age:18},{name:"張三",age:43}]
const summary = arr.reduce((pre, next) => pre + next.age, 0)  // summary : 61

陣列過濾指定資料

const arr = [{name:"lisi",age:17},{name:"張三",age:43}]
const underAgeArr = arr.filter(item=> item.age <= 18)  // underAgeArr [{name:"lisi",age:17}]
 

陣列對映一份自己需要的映象資料

const arr = [{name:"lisi",age:17},{name:"張三",age:43}]
const optionsList = arr.map(item=>{
  return {
    name:item.name,
    value: item.age
  }
})  // optionsList [{name:"lisi",value:17},{name:"張三",value:43}]

陣列遍歷,修改本陣列資料

const arr = [{name:"lisi",age:17},{name:"張三",age:43}]
arr.forEach(item=>{
  item.underAge = item.age <= 18
})  // arr [{name:"lisi",age:17,underAge: true},{name:"張三",age:43, underAge: false}]