Flash cards
Review the key moves
What is the main idea behind ECMAScript 2018?
Lesson checks
Practice each idea before moving on
Short Mimo-style checks built from this lesson's code, terms, and sequence.
Which statement best captures the main point of this lesson?
Complete the missing token from the example code.
___ await () {}Put the learning moves in the order that makes the concept easiest to apply.
New Features in JavaScript 2018
| Feature | Description |
|---|---|
| Asynchronous Iteration | Allows the await keyword in for/of loops |
| Promise Finally | Schedules a function to be executed when a promise has been "fulfilled" or "rejected" |
| Array Rest Elements | Allows to destruct an array and collect the leftovers |
| Object Rest Properties | Allows to destruct an object and collect the leftovers |
| Shared Memory | Allows different parts of a program to access the same memory |
New RegExp Features in 2018
| Feature | Description |
|---|---|
| /s | Allows the . (dot) metacharacter to match line terminators |
| \p{} | Matches character with a Unicode character property |
| (?<=y) | (?<=y)x matches "x" if "x" is preceded by "y" |
| (?<!y) | (?<!y)x matches "x" if "x" is NOT preceded by "y" |
| (?<name>) | Captures text and names (labels) it |
Browser Support
ECMAScript 2018 is supported in all modern browsers since Jun 2020 :
| Chrome 64 | Edge 79 | Firefox 78 | Safari 12 | Opera 51 |
|---|---|---|---|---|
| Jan 2018 | Jan 2020 | Jun 2020 | Sep 2018 | Feb 2018 |
JavaScript Asynchronous Iteration
ECMAScript 2018 added asynchronous iterators and iterables.
Example
for await () {}JavaScript Promise.finally()
ECMAScript 2018 finalizes the full implementation of the Promise object with Promise.finally :
Promise.finally() defines a function to be executed when a promise has either been successfully resolved rejected.
Example
let myPromise = new Promise();
myPromise.then();
myPromise.catch();
myPromise.finally();JavaScript Array Rest Elements
ECMAScript 2018 added the rest operator (...).
Example 1
let a, rest;
const arr1 = [1,2,3,4,5,6,7,8];
[a, ...rest] = arr1;Example 2
let a, b, rest;
const arr1 = [1,2,3,4,5,6,7,8];
[a, b, ...rest] = arr1;JavaScript Object Rest Properties
ECMAScript 2018 added the rest operator (...).
This allows us to destruct an object and collect the leftovers onto a new object:
Example
// Create an Object: const car = {type:"Fiat", model:"500", color:"white"}; // Destructure the Object
let {type, model, color} = car;
document.getElementById("demo").innerHTML = "The car type is: " + type;New JavaScript RegExp Features
ECMAScript 2018 added 4 new RegExp features:
- /s (dotAll) Flag
- Unicode Property Escapes (\p{...})
- Lookbehind Assertions (?<=y)x and (?<!y)x
- Named Capture Groups
RegExp /s Flag
Example
let text = "Line\nLine.";
let pattern = /Line./gs;
let result = text.match(pattern);The s (dotAll) flag allows the . (dot) metacharacter to match any character, including line terminator characters (like \n, \r, \u2028, \u2029).
Without s , \n does not match line terminators.
RegExp \p Metacharacter
Example
let text = "Hello 😄";
let pattern = /\p{RGI_Emoji}/v;
let result = pattern.test(text);The \p{Unicode Property} metacharacter matches any character with a Unicode character property.
RegExp Lookbehind
Example (?<=y)x
let text = "Hello ExampleSite";
let pattern = /(?<=Hello )ExampleSite/;
let result = pattern.test(text);(?<=y)x matches "x" if "x" is preceded by "y".
Negative Lookbehind
Example (?<!y)x
let text = "Hello ExampleSite";
let pattern = /(?<=Hello )ExampleSite/;
let result = pattern.test(text);(?<!y)x matches "x" if "x" is NOT preceded by "y".
RegExp Named Capturing Groups
Example (?<name>...)
const text = "Name: John Doe";
// Using named capturing groups
const regex = /(?<firstName>\w+) (?<lastName>\w+)/;
const match = text.match(regex);
let fName = match.groups.firstName;
let lName = match.groups.lastName;Explained
- (?<firstName>\w+) captures a word and labels it firstName
- (?<lastName>\w+) does the same for lastName
- text.match() returns an array with a groups property
- match.groups() returns an object: {firstName:"John", lastName:"Doe" }
When using a regular expression with capturing groups, the match() method of a string returns a result array that includes a groups property. This groups property is an object that holds the matches for named capturing groups.
JavaScript Threads
In JavaScript you use the Web Workers API to create threads.
Worker threads are used to execute code in the background so that the main program can continue execution.
Worker threads run simultaneously with the main program. Simultaneous execution of different parts of a program can be time-saving.
JavaScript Shared Memory
Shared memory is a feature that allows threads (different parts of a program) to access and update the same data in the same memory.
Instead of passing data between threads, you can pass a SharedArrayBuffer object that points to the memory where data is saved.
SharedArrayBuffer
A SharedArrayBuffer object represents a fixed-length raw binary data buffer similar to the ArrayBuffer object.