ES2019 Made Error Checking Easier in JavaScript

ES2019 Made Error Checking Easier in JavaScript

The ECMAScript2019 specification means it is now optional to use the error parameter inside the catch block of a try…catch statement.

Originally published by Dr. Derek Austin at

Before recent changes to JavaScript language, a try…catch statement always needed the caught error to be referenced inside the catch block.

In modern JavaScript, referencing the caught error is now optional.

Let’s look at a demo on processing JSON objects to see how it works.

// Let's take this JavaScript object and turn it into JSON
// Stringify should work -- it turns objects to JSON strings
// Parse should fail -- it turns JSON strings to objects
const myJavaScriptObject = {
  dog: "🐕",
  cat: "🐈",
  koala: "🐨",
  count: 3

// Before ES2019 -- Need to reference caught error try { console.log(JSON.parse(myJavaScriptObject)); } catch (error) { console.log(error + ""); } // result: SyntaxError: JSON.parse: unexpected character at line 1 column 2 of the JSON data

// Works in ECMAScript2019 -- Leave out error try { console.log(JSON.parse(myJavaScriptObject)); } catch (error) { console.log("Whoops! That did not seem to be a JSON String... "); } // result: Whoops! That did not seem to be a JSON String...

// ES2019: No error, no problem -- we don't even really have to "catch it" as a parameter try { console.log(JSON.stringify(myJavaScriptObject)); } catch { console.log("Whoops! That did not seem to be a JSON String... "); } // result: {"dog":"🐕","cat":"🐈","koala":"🐨","count":3}

Not sure how JSON.parse() works?

Try…catch statements are commonly used with promises and asynchronous functions

The Takeaway

Is not referencing caught errors always useful? No, of course not. There are times when you do want to display the caught error itself.

However, there are cases where the error is not particularly informative, such as the SyntaxError that comes from JSON.parse().

In those cases, it can be useful to not reference the caught error by name.

Thanks for reading

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The Complete JavaScript Course 2019: Build Real Projects!

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