function sum(arr) {
return arr.reduce((pre, next) => pre + next, 0)
} function sum(arr) {
let a = 0;
for (let i =0; i< arr.length; i ++) {
a +=arr[i]
}
return a
} function sum(arr) {
return arr.reduce((i,j)=>{
return i+j;
})
}