Brayan Arrieta Alfaro
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New JavaScript Features ECMAScript 2022 (with examples)

New JavaScript Features ECMAScript 2022 (with examples)

Brayan Arrieta Alfaro
·May 16, 2022·

6 min read

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ECMAScript 2022 is the version of ECMAScript corresponding to this year. There are some new features that have been incorporated and could be used in our javascript projects. Also if you want to see the ES2021 I had created the next blog post for that New JavaScript Features ECMAScript 2021 (with examples)

The new ECMAScript features for this year are:

  • Top-level await
  • Private instance fields, methods, and accessors
  • Static class fields and methods
  • Static class initialization blocks
  • Error: .cause
  • Array, String, and TypedArray: .at() Method
  • Object: .hasOwn()
  • RegExp: match .indices ('d' flag)

Top-level await

Until this point, we could only use await in the scope of async functions. This was fine until it wasn't, like when we hit the top level of our module and could not use the await keyword. Now the await can be used at the top level of a module and can be super handy when initializing imports and creating fallbacks.

Example

The old behavior

When the async/await feature was first introduced, attempting to use an await outside of an async function resulted in a SyntaxError. Many developers utilized as an alternative IIFE (Immediately Invoked Function Expression) as a way to get access to the feature.

await Promise.resolve(console.log('Hello World'));
// Output: SyntaxError: await is only valid in async function

// Alternative to fix the problem
(async function() {
  await Promise.resolve(console.log('Hello World'));
  // Output: Hello World
}());

The new behavior

With top-level await, we don't need to use more life hacks.

await Promise.resolve(console.log('Hello World'));
// → Hello World

Use cases

Dynamic dependency pathing

const strings = await import(`/i18n/${navigator.language}`);

This allows for Modules to use runtime values in order to determine dependencies. This is useful for things like development/production splits, internationalization, environment splits, etc.

Resource initialization

const connection = await dbConnector();

This allows Modules to represent resources and also to produce errors in cases where the Module will never be able to be used.

Dependency fallbacks

let jQuery;
try {
  jQuery = await import('https://cdn-a.com/jQuery');
} catch {
  jQuery = await import('https://cdn-b.com/jQuery');
}

Private instance fields, methods, and accessors

Previously when was needed to declare a private method or field needs to be added an underscore at the beginning of the method name (based on convention), however, that does not guarantee that the method will be private.

With ES2022 was added as new features as private instance fields, methods, and accessors. We need to add just # at the beginning of the method name and in that way will be declared as private.

Private class fields

Example

class Test {
  #firstName = 'test-name';
}

const test = new Test();
test.firstName

// Output: undefined

Private class methods

Example

class Test {

  #addTestRunner(testRunner){
    this.testRunner = testRunner
  }
}

const test = new Test();
test.addTestRunner({name: 'test'});

// Output: TypeError: test.addTestRunner is not a function

Private accessors (getters and setters)

Previously when was needed to declare a getter or setter can be accessed by means of the instance created, with ES2022 was added as a new feature the private accessors.

Example

class Test {

  get #name(){
    return 'test-name';
  }
}

const test = new Test();
test.name

// Output: undefined

Static class fields and methods

Static class fields and methods are not used on instances of a class. Instead, can be called on the class itself and is declared using the static keyword.

Static methods are often utility functions, and helpers, whereas static properties are useful for caches, fixed-configuration, or any other data we don’t need to be replicated across instances.

Examples

Static class fields

class Test {
  static firstName = 'test-static-name';
}

Test.firstName

// Output: test-static-name

Static class methods

class Test {
  static greeting(){
    console.log('Hello this is a greeting from a static method');
  }
}

Test.greeting();

// Output: Hello this is a greeting from a static method

Note: We are using in these examples as static public fields and methods, however, we can create also static private fields and methods.

Static class initialization blocks

This new feature provides a mechanism for additional static initialization during class definition evaluation.

Example

class Test {
  static numbers = [1,2,3,4,5,6];
  static evenNumbers = [];
  static oddNumbers = [];

  // static class initialization block
  static {
   this.numbers.forEach((number) => {
     if(!(number % 2) ) {
       this.evenNumbers.push(number);
     } else {
        this.oddNumbers.push(number);
     }
   });
  }
}

Test.evenNumbers;
// Output: [2, 4, 6]

Test.oddNumbers;
// Output: [1, 3, 5]

Error: .cause

Error and its subclasses now let us specify the reason behind the error. Sometimes, we catch errors that are thrown during more deeply nested function calls and would like to attach more information to them.

With the Error cause, we can add more intrinsic information for our errors. To use this new feature, we should specify the error options as a second parameter, and with the cause key we can pass the error that we want to chain.

Example

const getUsers = async(array)=> {
  try {
    const users =  await fetch('https://myapi/myusersfake');
    return users;
  } catch (error) {
    console.log('enter')
    throw new Error('Something when wrong, please try again later', { cause: error })
  }
}

try{
  const users = await getUsers();
} catch(error) {
  console.log(error); // Error: The array need a minimum of two elements
  console.log(error.cause); // TypeError: Failed to fetch
}

Array, String, and TypedArray: .at() Method

Until this point, programmers have asked for the ability to do negative indexing of JS Arrays, as you can do with other programming languages. That is, asking for the ability to write arr[-1] instead of arr[arr.length-1], where negative numbers count backward from the last element.

This year with ECMAScript 2022 we have a big change with a new method that helps programmers with the negative indexing, the .at() method that is supported by Array, String, or TypedArray.

Example

Access the latest element of the Array and String

The old behavior

const fruitsArray = ['banana', 'apple', 'orange', 'kiwi'];
console.log(fruitsArray[fruitsArray.length -1])
// Output: kiwi

const fruit = 'kiwi';
console.log(fruit[fruit.length -1])
// Output: i

The new behavior

const fruitsArray = ['banana', 'apple', 'orange', 'kiwi'];
console.log(fruitsArray.at(-1))
// Output: kiwi

const fruit = 'kiwi';
console.log(fruit.at(-1))
// Output: i

Note: The .at() also accepts positive numbers, so it can be used as another way when indexing is required.

Object: .hasOwn()

Today, it is very common (especially in library code) to write code like

let hasOwnProperty = Object.prototype.hasOwnProperty

if (hasOwnProperty.call(object, "foo")) {
  console.log("has property foo")
}

This new feature simplifies that code to

if (Object.hasOwn(object, "foo")) {
  console.log("has property foo")
}

RegExp: match .indices ('d' flag)

The new /d flag feature provides some additional information about the start and indices position end of each match in the input string.

Example

Without the /d flag

const regexExample = /greeting(\d)/g;
const exampleString = 'greeting1greeting2';
const result = [...exampleString.matchAll(regexExample)];
console.log(result[0]);

Output

Without d flag output

With the /d flag

const regexExample2022 = /greeting(\d)/dg;
const exampleString = 'greeting1greeting2';
const result = [...exampleString.matchAll(regexExample2022)];
console.log(result[0]);

Output

With d flag output

When we use the /d flag we have an array with the indices of the different elements that match the regex.

Conclusion

JavaScript is an awesome programing language. Every year there is a new awesome feature that can be used in our projects. In this post, we’ve reviewed the ES2022 features. We expect surprises the next year with a new version ES2023. Also if you want to see the ES2021 I had created the next blog post for that New JavaScript Features ECMAScript 2021 (with examples)

Let me know in your comments recommendations or something else that can be added, I will update the post based on that thanks! 👍

References

 
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