错误TS2356表示数字类型变量必须是“Number”类型的算术操作数

timeLeft: Number;

constructor() { 
    this.timeLeft = 60;
  }

  start() {
    console.log(typeof(this.timeLeft)); // prints out 'number'

    setInterval(() => {

      this.timeLeft--; // error TS2356 occurs here
      console.log(this.timeLeft);

    }, 1000);
  }

  ngOnInit() {}

慰问:

错误TS2356:算术操作数必须是“any”、“number”或枚举类型。