May 2018
Intermediate to advanced
190 pages
2h 19m
English
book
Practical ES6
by Aurelio De Rosa, Kyle Pennell, Nilson Jacques, Craig Buckler, Byron Houwens, Jeff Mott, Sandeep Panda, Graham Cox, Ludovico Fischer, James Wright
Content preview from Practical ES6
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Chapter 1: New Keywords: let and const
by Aurelio de Rosa
In this tutorial, I'll introduce let and const, two new keywords added to JavaScript with the arrival of ES6. They enhance JavaScript by providing a way to define block-scope variables and constants.
let
Up to ES5, JavaScript had only two types of scope, function scope and global scope. This caused a lot of frustration and unexpected behaviors for developers coming from other languages such as C, C++ or Java. JavaScript lacked block scope, meaning that a variable is only accessible within the block in which it’s defined. A block is everything inside an opening and closing curly bracket. Let's take a look at the following example:
function foo() { var par = 1; if (par >= 0) { var bar = ...Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.