Recently all major browsers updated their JavaScript features. So in this post, I will dive into these six features worth mentioning to improve your JavaScript skills in 2022.
These features are both very new features and features that improve the already existing functionality in JavaScript.
1. Get JavaScript Array item with Array.at()
Before
Let’s start with the Array.at() method. Since the early days of JavaScript, we have been using this syntax to get a specific element with a known index from an Array.
const array = [0, 1,2,3,4,5,6,7,8,9]
const firstElement = array[0];
const fourthElement = array[3]
const lastElement = array[array.length - 1];
const thirdLastElement = array[array.length - 3];
After
For now, this works perfectly fine. But array.at() can be more readable. So with this method, we can write the code from above in a more readable manner.
const array = [0, 1,2,3,4,5,6,7,8,9]
const firstElement = array.at(0);
const fourthElement = array.at(3)
const lastElement = array.at(-1);
const thirdLastElement = array.at(-3);
The syntax becomes shorter, especially with the last or nth-last elements.
If the Array index doesn’t exist, you still get an undefined value back, so nothing has changed there.
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Browser support
The browser support is perfect, in my opinion. Hopefully, you don’t need to support old Internet Explorer browsers because they lack support. Find more information and examples in de MDN Web Docs.
2. Deep copy a JavaScript Object with structuredClone()
If you want to create a copy of a JavaScript Object, it becomes a shallow copy most of the time.
Spread operator copy
const myBrowser = {
language: 'JavaScript',
framework: 'Angular',
browser: 'Brave',
os: 'Windows 11',
date: {
time: new Date().getTime(),
date: null
}
}
const myBrowserShallowCopy = {...myBrowser};
console.log('before myBrowser:', myBrowser);
console.log('before myBrowserShallowCopy:', myBrowserShallowCopy);
myBrowserShallowCopy.browser = 'Chrome';
console.log('after update myBrowser:', myBrowser);
console.log('after update myBrowserShallowCopy:', myBrowserShallowCopy);
myBrowser.date.date = new Date();
console.log('after update original myBrowser:', myBrowser);
console.log('after update original myBrowserShallowCopy:', myBrowserShallowCopy);
This means that updating a nested property (not a top-level property) will also affect the shallow copy.
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JSON Parse & Stringify
Making deep copies require something more. We need JSON.parse(JSON.stringify(object)) for that. It feels like a hack, but it gets the job done.
const myBrowser = {
language: 'JavaScript',
framework: 'Angular',
browser: 'Brave',
os: 'Windows 11',
date: {
time: new Date().getTime(),
date: null
}
}
const myBrowserCopy = JSON.parse(JSON.stringify(myBrowser));
console.log('before myBrowser:', myBrowser);
console.log('before myBrowserCopy:', myBrowserCopy);
myBrowserCopy.browser = 'Chrome';
console.log('after update myBrowser:', myBrowser);
console.log('after update myBrowserCopy:', myBrowserCopy);
myBrowser.date.date = new Date();
console.log('after update original myBrowser:', myBrowser);
console.log('after update original myBrowserCopy:', myBrowserCopy);
When you run this code, you will see that the original myBrowser is being updated, but the deep copy myBrowserCopy is not updated. So with JSON.parse(JSON.stringify(object)) you can create deep copies.
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StructuredClone()
You can use a more straightforward method to create deep copies of your objects.
const myBrowser = {
language: 'JavaScript',
framework: 'Angular',
browser: 'Brave',
os: 'Windows 11',
date: {
time: new Date().getTime(),
date: null
}
}
const myBrowserCopy = structuredClone(myBrowser);
console.log('before myBrowser:', myBrowser);
console.log('before myBrowserCopy:', myBrowserCopy);
myBrowserCopy.browser = 'Chrome';
console.log('after update myBrowser:', myBrowser);
console.log('after update myBrowserCopy:', myBrowserCopy);
myBrowser.date.date = new Date();
console.log('after update original myBrowser:', myBrowser);
console.log('after update original myBrowserCopy:', myBrowserCopy);
As you can see, this method has better readability because it says you make a clone of that object.
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Browser support
The browser support is great, in my opinion. Hopefully, you don’t need to support old Internet Explorer browsers because they lack support. Also, keep in mind that some browsers don’t support this method for workers. Find more information and examples in de MDN Web Docs.
3. Top-level await
Since ES2017, we have async/await for synchronously writing Promises.
Before
The only condition there was to use await in JavaScript. You needed to make your function async, which is sometimes a bit of a hassle. Because you don’t want to write async before every function that uses await, right?
(async function() {
const one = () => {
return new Promise((resolve) => {
setTimeout(() => resolve(2), 2000);
})
};
console.log(await one());
}());
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Writing a iffe for every time you wanted to use await is also pretty ugly 🤭. When the code doesn't run, select the newest Node version 👆
After
Well, since now we can use await without using async 💪
const one = () => {
return new Promise((resolve) => {
setTimeout(() => resolve(2), 2000);
})
};
console.log(await one());
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Now you don’t need any iffe boilerplate anymore 🔥. We need to write await; that’s it 😀! Remember that methods in Classes still need to have the async keyword before it; otherwise, it won’t work.
Browser support
In my opinion, the browser support is great. Hopefully, you don’t need to support old Internet Explorer browsers because they lack support. Find more information and examples in de V8 documentation.
4. For await of
I don’t know if this use case ever happened to you, but for me, it did.
Imagine you need to make multiple AJAX calls after each other, but you want to loop over them. But during the loop, those Promises are not resolved yet. So what are you going to do?
Before
A while ago, it was only possible to wait until all those Promises were resolved. After the resolvent, you could loop over them.
const one = () => {
return new Promise((resolve) => {
setTimeout(() => resolve(2), 2000);
})
};
const two = () => {
return new Promise((resolve) => {
setTimeout(() => resolve(3), 3000);
})
};
const three = () => {
return new Promise((resolve) => {
setTimeout(() => resolve(5), 5000);
})
};
const four = () => {
return new Promise((resolve, reject) => {
setTimeout(() => reject(6), 6000);
})
};
// This async IFFE is only needed in NodeJS
(async () => {
try {
const allPromises = await Promise.all([one(), two(), three(), four()]);
for (const result of allPromises) {
console.log('result:', result)
}
} catch (e) {
console.log('caught', e);
}
})();
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While running this code, you can see that if one of the Promises will not be resolved but rejected, the for-loop doesn’t even begin to loop over them.
After
But thanks to the for await...of you can combine a for-loop with the Promise.all() functionality.
const one = () => {
return new Promise((resolve) => {
setTimeout(() => resolve(2), 2000);
})
};
const two = () => {
return new Promise((resolve) => {
setTimeout(() => resolve(3), 3000);
})
};
const three = () => {
return new Promise((resolve) => {
setTimeout(() => resolve(5), 5000);
})
};
const four = () => {
return new Promise((resolve, reject) => {
setTimeout(() => reject(6), 6000);
})
};
const arr = () => {
return [one(), two(), three(), four()];
}
// This is only needed in NodeJS
(async () => {
try {
for await (const result of arr()) {
console.log('result:', result)
}
} catch (e) {
console.log('caught', e);
}
})();
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As you can see, this is better to read in my opinion. And every time a Promise is resolved, the loop goes to the following Promise, which is excellent!
But when a Promise gets rejected, the for-loop will stop. If you want the loop to continue when a Promise is rejected, you need to use Promise.allSettled(). With this method, you can see which promises are rejected and fulfilled. (Check MDN Web Docs for more information about Promise.allSettled)
const one = () => {
return new Promise((resolve) => {
setTimeout(() => resolve(2), 2000);
})
};
const two = () => {
return new Promise((resolve, reject) => {
setTimeout(() => reject(3), 3000);
})
};
const three = () => {
return new Promise((resolve) => {
setTimeout(() => resolve(5), 5000);
})
};
// This async IFFE is only needed in NodeJS
(async () => {
const promisesArr = [one(), two(), three()];
const allPromises = await Promise.allSettled(promisesArr).then((promises) => {
for (const result of promises) {
console.log('result:', result)
}
}, (error) => console.error(error));
})();
When the code doesn't run, select the newest Node version 👆or try it on Runkit
Browser support
In my opinion, the browser support is great. Hopefully, you don’t need to support old Internet Explorer browsers because they lack support. Find more information and examples in de MDN Web Docs.
5. Private class fields
Every developer that spends some time in TypeScript knows the privatekeyword. This tells that a property or method is only used inside that class. But in the browser, you can see that those fields and methods are exposed just like the public ones.
From now on, we can make a property of method private by putting a # before it. It’s not only syntactic sugar, but it doesn’t expose that field or method to the outside.
class MyCoolClass {
publicField = 'This fields is visible outside the class';
#privateField = 'This field is hidden outside the class';
getPrivateField() {
return this.#privateField;
}
}
const myClass = new MyCoolClass();
console.log('myClass :', myClass);
// myClass : MyCoolClass {
// publicField: "This fields is visible outside the class"
/// #privateField: "This field is hidden outside the class"
// [[Prototype]]: Object
// constructor: class MyCoolClass
// getPrivateField: ƒ getPrivateField()
console.log('myClass.publicField :', myClass.publicField);
// myClass.publicField : This fields is visible outside the class
console.log('myClass.#privateField :', myClass.#privateField);
// Uncaught SyntaxError: Private field '#privateField' must be declared in an enclosing class
console.log('myClass.getPrivateField():', myClass.getPrivateField());
// 'This field is hidden outside the class'
Sorry no Runkit embed, the private class fields are not supported by them ☹️
If you log the whole class in the console, you can see that the private field exists, but when you try to call it, you receive a syntax error. Private fields can be exposed outside the class with a public method.
Browser support
In my opinion, the browser support is great. Hopefully, you don’t need to support old Internet Explorer browsers because they lack support. Find more information and examples in de MDN Web Docs.
6. Object.hasOwn
Sometimes we like to check if an Object has a specific property before we try to access it. Yes, I know that there is something like optional chaining 😉.
If you have to check these things a lot of times, please consider TypeScript. Follow my TypeScript for Beginners guide.
For years we have the Object.prototype.hasOwnProperty() method in JavaScript. This method returns a boolean when you use it.
const obj = {
propA: 'Value',
propB: false
}
console.log('propA:', obj.hasOwnProperty('propA')); // "propA: true"
console.log('propC:', obj.hasOwnProperty('propC')); // "propA: false"
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But when we try to make an Object like this, it will become confusing.
const obj = Object.create(null);
obj.propA = 'Value';
obj.propB = false;
console.log('propA:', obj.hasOwnProperty('propA')); // Uncaught TypeError: obj.hasOwnProperty is not a function
console.log('propC:', obj.hasOwnProperty('propC')); // Uncaught TypeError: obj.hasOwnProperty is not a function
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Because usually, when you create an Object (const obj = {}), that Object gets all default properties and methods from Object.prototype, but when you give null as a value to the create method, it won’t receive anything from Object.prototype so that’s why the hasOwnProperty method isn’t on that Object.
With the Object.hasOwn, you don’t have that problem.
const obj = Object.create(null);
obj.propA = 'Value';
obj.propB = false;
console.log('propA:', Object.hasOwn(obj, 'propA'));
console.log('propC:', Object.hasOwn(obj, 'propC'));
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Browser support
Note:
Object.hasOwn()is intended as a replacement for[Object.hasOwnProperty()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/hasOwnProperty).
In my opinion, the browser support is great. Hopefully, you don’t need to support old Internet Explorer browsers because they lack support. Find more information and examples in de MDN Web Docs.
Thanks!
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