8 JS reduce usage examples and reduce operation methods

// Accumulate [1, 2, 3, 4, 5, 6, 7, 8].reduce((a, i) => a + i);
// Output: 36

// Accumulate, with a default initial value of [1, 2, 3, 4, 5, 6, 7, 8].reduce((a, i) => a + i, 5);
// Output: 41

// Accumulate [1, 2, 3, 4, 5, 6, 7, 8].reduce((a, i) => a * i);
// Output: 40320

[1, 2, 3, 4, 5, 6, 7, 8].reduce((a, i) => Math.max(a, i));

Math.max(...[1, 2, 3, 4, 5, 6, 7, 8]);

let data = [
  ["red","128g","iPhone"],
  ["North-South","Two bedrooms and one living room","128㎡","Western-style house"],
  ["Xiaomi","white","smart sports watch","heart rate, blood pressure, blood oxygen","call message reminder"], 
  ["Official Release","Autumn 2020","Basketball","Sneakers","Brand Direct Mail"]
]
let dataConcat = data.map(item=>item.reduce((a,i)=>`${a} ${i}`))

// Output:
["Red 128g Apple mobile phone"
"North-South two-bedroom and one-living room 128㎡ Western-style house"
"Xiaomi white smart sports watch heart rate, blood pressure, blood oxygen, call information reminder"
"Official sale of 2020 autumn basketball shoes brand direct mail"]

let array = [1, 2, 3, 'a', 'b', 'c', 1, 2, 3, 'a', 'b', 'c'];
array.reduce((noDupes, curVal) => {
  if (noDupes.indexOf(curVal) === -1) { noDupes.push(curVal) }
  return noDupes
}, [])

// Output: [1, 2, 3, 'a', 'b', 'c']

[..."(())()(()())"].reduce((a,i)=> i === '(' ? a+1 : a-1 , 0);
// Output: 0

// Using loop method let status=0
for (let i of [..."(())()(()())"]) {
  if(i === "(")
    status = status + 1
  else if(i === ")")
    status = status - 1
  if (status < 0) {
    break;
  }
}

let obj = [
  {name: '张三', job: 'Data Analyst', country: '中国'},
  {name: 'Ace', job: 'Scientist', country: 'China'},
  {name: 'Leir', job: 'Scientist', country: 'United States'},
  {name: 'Bob', job: 'Software Engineer', country: 'India'},
]

obj.reduce((group, curP) => {
  let newkey = curP['country']
  if(!group[newkey]){
    group[newkey]=[]
  }
  group[newkey].push(curP)
  return group
}, [])
// Output:
[ China: [{…}, {…}]
  India: [{…}]
  USA: [{…}] ]

[[3, 4, 5], [2, 5, 3], [4, 5, 6]].reduce((singleArr, nextArray) => singleArr.concat(nextArray), [])
// Output: [3, 4, 5, 2, 5, 3, 4, 5, 6]

[ [3, 4, 5], 
 [2, 5, 3], 
 [4, 5, 6]
].flat();

[..."hello world"].reduce((a,v) => v+a)

[..."hello world"].reverse().join('')