SOURCE

let arr=[1,2,,3,4];
arr.forEach((item,index,arr)=> arr[index]=item+1);
console.log(arr)
let arr2=arr.map((item,index,arr)=> arr[index]=item+1);
console.log(arr2)
console.log(arr2.filter(x => x>3))
console.log(arr2.find(x => x>3))
let a=[
    {
        name:'yjk'
    },
    {
        age:12
    }
]
let b=new Array(6)
b.fill(0)
b.fill(7,4,-1)
console.log(b)

let c={}
let sum=1;
while(sum < 10){
    c[sum]=sum
    sum+=1
}
c.length=sum
let total=''
for(let i=0;i<c.length;i++){
    total += c[i]
}
console.log(total)