类型 'number | 上不存在属性 'getTime' 日期'

Question

class SW {
    private startTime: number | Date
    private endTime: number | Date

    constructor() {
        this.startTime = 0,
        this.endTime = 0
    }
    start() {
        this.startTime = new Date();    
    }
    stop() {
        this.endTime = new Date();   
    }

    getDuration() {
        const seconds = (this.endTime.getTime() - this.startTime.getTime()) / 1000;
    }
}

Now I have this error: Property 'getTime' does not exist on type 'number | Date'. Property 'getTime' does not exist on type 'number | Date'.

Based on this Link I also tried to declare Date but didn't work.

interface Date {
    getTime(): number
}

Any idea would be appreciated.

Answer 1

Your property is declared as number | Date number | Date , meaning it could be either. In your constructor, it's a number. Later, when you call start , you change it from number to Date . In getDuration , TypeScript has no way of knowing what it is ( number or Date ).

From looking at your code, you may want to always use number by using Date.now() instead of new Date() and then not using getTime :

class SW {
    private startTime: number;
    private endTime: number;

    constructor() {
        this.startTime = 0,
        this.endTime = 0
    }
    start() {
        this.startTime = Date.now();    
    }
    stop() {
        this.endTime = Date.now();   
    }

    getDuration() {
        const seconds = (this.endTime - this.startTime) / 1000;
    }
}

You might also consider having getDuration either throw an error or return NaN when this.endTime or this.startTime is 0 .

Answer 2

Just make it simple

class SW {
  private startTime: number;
  private endTime: number;
 
  start() {
    this.startTime = new Date().getTime(); 
  }
  stop() {
    this.endTime = new Date().getTime();
  }

  getDuration() {
    return (this.endTime - this.startTime) / 1000;
  }
}