题目：打印输出九九乘法表

const dom = document
for (let i = 1; i <= 9; i++) {
  for (let j = 1; j <= i; j++) {
    const res = `${j} * ${i} = ${j*i};&nbsp;&nbsp;&nbsp;`
    dom.write(res)
    if (i == j) dom.write('<br/>')
  }
}