JavaScript && Operator used for returns

Question

I am working understanding a JavaScript library and I came across this statement:

const assetsManifest = process.env.webpackAssets && JSON.parse(process.env.webpackAssets)

Then later on in the library, it uses the assetsMannifest like an object e.g.

assetsManifest['/vendor.js']

I thought the && operator was only used to return boolean values in logical checks. Can someone explain to me what is going on here?

Many thanks,

Clement

Answer 1

This operator doesn't always return true or false. It doesn't work like in some other programming languages. In JavaScript && operator returns the first value if it's falsy or the second one if not.

Examples:

null && 5 returns null because null is falsy.

"yeah yeah" && 0 returns 0 because every string is truthy.

Not so obvious :-)

Further reading:

Why don't logical operators (&& and ||) always return a boolean result?