How to make a timer with a context manager

README.md

Timer

This is some sample code that shows how use a design pattern to implement a timer.

To use:

• Create the new Timer instance, indicating time
• call .body on the instance, where the first parameter is the function to execute
• periodically within that function, call this.check() which will raise TimeUpErr error if the duration has expired

function myFunction() {
  const timer = new Timer({seconds: 2});
 
  timer.body(function () {
    for (let x = 0; x < 2000000; x++) {
      if (x % 1000 === 0) {
        Logger.log('zzzz');
        Utilities.sleep(1000);
        this.check();
      }
    }
    Logger.log('loop done');
  });
}

timer.gs

class TimeUpErr extends Error {
}


class ContextManager {
  
  enter () {
    // set up state
  }
  
  error (err) {
    return null;  // returning null indicates we don't want to re-raise it in exit block
  }

  exit () {
    // we
  }
  
  body (func) {
    let result;
    
    // execute the enter function
    this.enter();
    
    try {
      
      // bind it so we can access via `this`
      result = func.call(this);
      
    } catch (err) {
      // execute the error handler
      // error handler can return null to indicate it should be swallowed
      const swallow = this.error(err) === null;
      
      // if error happened, call error function
      // if it returns null swallow it, otherwise reraise
      if (!swallow)
        throw err;
      
    } finally {
      
      // execute the exit
      this.exit();
    }
    
    return result;
  }
}
  
class Timer extends ContextManager {
  constructor ({seconds=10, minutes=0}={}) {
    super();
    this.milliseconds = (seconds * 1000) + (minutes * 60 * 1000);
  }
  
  enter () {
    this.start = new Date();
    this.timeup = false;
  }
  
  exit () {
    if (this.timeup) {
      Logger.log('inform user');
    }   
  }
  
  error (err) {
    if (err instanceof TimeUpErr) {
      return null;  // swallow it
    }
    Logger.log(err.message); 
  }
  
  check () {
    const now = new Date();
    if (now.getTime() - this.start.getTime() >= (this.milliseconds)) {
      this.timeup = true;
      throw new TimeUpErr('Time is up');
    }
  }
}