try catch 没有得到 date-fns parseISO 错误

Question

there seems a simple mistake by me, I wrote this code to get a formatted date but if date dosn't have correct string to convert, class should catch the error but it doesn't work and an error is shown in console !

import {format,parseISO} from 'date-fns';

class DateFormats {
  // class methods
  constructor(date) { 
    try{
      this.parsedDate = parseISO(date);      
    }
    catch(e){
      this.parsedDate = new Date();
      console.log('catch Error')
    }
   }
 
   get MMM_d_YYYY() {
     return format(this.parsedDate, "MMM d,yyyy")
    }
 
}
 

const wrongDate='2020-*12-20T04:18:21.471275';

console.log(new DateFormats(wrongDate).MMM_d_YYYY);

error in console:

RangeError: Invalid time value

any idea?

Answer 1

try..catch should only be used as a last resort so should only be used when there's no other option.

If a function requires arguments of a particular type, then check before calling it, don't just use try..catch and deal with errors afterward. In this case, the date-fns parseISO function requires a string to avoid a typeError, so ensure it's called with a string or perhaps return undefined or similar value. Then the caller can check the response and deal with it.

In this case, if the catch block is executed, then:

this.parsedDate = 'error';

is executed, so when MMM_d_YYYY is accessed/called it calls format on a string when it's expecting a Date object, so date-fns throws an error.

Avoid both errors by checking before calling the functions, not catching errors afterward.

If you start using try..catch to handle inappropriate input, you force the caller to also use try..catch , so it starts to propagate through your code. By handling incorrect input (eg by simply returning an Invalid Date), then the caller can check the return value using an if block and deal with "errors" that way, which is much more economical that try..catch .

It's also nice to provide a default where no argument is passed, in this case the current date and time seems appropriate, so:

let format = require('date-fns/format')
let parseISO = require('date-fns/parseISO')

class DateFormats {

  // class methods
  // Default is current date and time
  constructor(arg = new Date().toISOString()) {

    // Ensure arg is a string and let date-fns deal with parsing it
    // This might result in an invalid Date, but let the caller
    // deal with that
    this.parsedDate = parseISO(String(arg));
   }
 
   // Return timestamp in MMM d YYYY format or "Invalid Date"
   get MMM_d_YYYY() {

     // this.parsedDate might be an invalid Date, so check first
     // as calling format on an invalid date throws an error
     if (isNaN(this.parsedDate)) {
       return this.parsedDate.toString(); // Invalid Date
     }

     // Otherwise, it's a valid Date so use it
     return format(this.parsedDate, "MMM d,yyyy")
    } 
}
 
// Examples
[void 0,                       // default, no arg   -> Jan 31,2021
 '2020-12-20T04:18:21.471275', // valid timestamp   -> Dec 20,2020
 'fooBar'                      // invalid timestamp -> Invalid Date
].forEach(arg => console.log(arg + ' -> ' + (arg? new DateFormats(arg).MMM_d_YYYY : new DateFormats().MMM_d_YYYY)));

The above can be run at npm.runkit

Answer 2

When You passing the wrong date it is going to catch. At correct place but in cache you are passing the string "error" in the variable this.parsedDate and when you are calling gettter MMM_d_YYYY what getter is trying to compile is

//Value of this.parsedDate which is 'error' because of catch
return format('error', "MMM d,yyyy")

This function is throwing an error. because 'error' string can not be formattable.

import {format,parseISO} from 'date-fns';

class DateFormats {
  // class methods
  constructor(date) { 
    try{

      this.parsedDate= parseISO(date);
    }
    catch(e){
      this.parsedDate=parseISO(new Date());
      console.log(this.parsedDate)
    }
   }
 
   get MMM_d_YYYY() {
     return format(this.parsedDate, "MMM d,yyyy")
    }
 
}
 

const wrongDate='2020-12-20T04:18:21.471275';

console.log(new DateFormats(wrongDate).MMM_d_YYYY);