Logical Assignment Operators

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I love JavaScript, it's my favorite programming language, but I love dipping into other languages because they offer a new perspective on coding paradigms. There've been syntax additions to JavaScript that I've seen I found interesting (think ?? in optional chaining) and now we get more -- logical assignment operators. Let's check out how they can be used!


Or-Or-Equals is used to assign a value when one doesn't exist:

let name;
const defaultName = "Guest";

name ||= defaultName;
// name >> "Guest"

// Equivalent: name || (name = defaultName);


Question-Question-Equals assigns value when the value is undefined:

const j = 1;
j??= 10
// j >> 1

x = undefined;
x ??= 10
// x >> 10


And-And-Equals assigns value to the last in line when both are defined:

let name;
const defaultName = "Guest";

name &&= defaultName;
name >> undefined

// Both have values
let name = "David";
const defaultName = "Guest";

name &&= defaultName;
// name >> "Guest"

// Equivalent: name && (name = defaultName);

I do worry, at least in the short term, that this new syntax could be hard to maintain, but just like every other new language feature, we'll get used to it!

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