for .in 语法不支持，该怎么办啊？

copyRecord(source: Record<string, string>): Record<string, string> { 
  const target: Record<string, string> = {}; 
  // 遍历源对象的属性 
  let sourceKeys = Object.keys(source) 
  let targetKeys = Object.keys(target) 
  for (let i = 0;i<sourceKeys.length;i++) { 
    if (targetKeys.indexOf(sourceKeys[i])>=0) { 
      // 复制到目标对象 
      target[sourceKeys[i]] = source[sourceKeys[i]]; 
    } 
  } 
  return target; 
}