Segitiga.js

const solution = (n) => {
  let x = []
  let y = []

  for(let j = n; j > 0; j--){
    for(let i = 0; i < j; i++){
      x.push('*')
    }
    console.log(x.join(''))
    x = []
  }

  for(let j = 1; j < n; j++){
    for(let i = -1; i < j; i++){
      y.push('*')
    }
    console.log(y.join(''))
    y = []
  }
}

solution(10)