报错如下:
Uncaught TypeError: Cannot read property 'length' of undefined
请问是哪里出问题了, 该怎么解决, 谢谢
html

  changeIndex (index){
    console.log(index)
    this.activeIndex = index
    this.sportDatabaseOrderBy = this.sportDatabase.slice(0) // 数组深拷贝
    for (let i = 0; i < this.sportDatabaseOrderBy.length; i++) {
       let firstLetter = py.getFullChars(this.sportDatabaseOrderBy[i].name).slice(0,1)
       this.sportDatabaseOrderBy[i].firstLetter = firstLetter
    }
  }