ES6 module live bindings: surprise!

ES6 modules are pretty common in new JavaScript projects. They include one feature that can be pretty surprising to folks used to CommonJS modules: live bindings.

Consider the following CommonJS app you want to port to ES6:

// my-library.js
let name = 'default';

function setName(n) {
  name = n;
}

module.exports = { name, setName };

// my-app.js
var { name, setName } = require('./my-library');

console.log( name );
setName( 'ben' );
console.log( name );

That would print:

default
default

A quick port to ES6 might look like this:

// my-library.js
let name = 'default';

function setName(n) {
  name = n;
}

export { name, setName };

// my-app.js
import { name, setName } from './my-library';

console.log( name );
setName( 'ben' );
console.log( name );

But this will print:

default
ben

name changed without anything in my-app.js touching it directly.

This can be useful behavior, but it can also be pretty surprising.

Always plan for seasonal movement

This takes seasonal movement, a common problem in woodworking, to a whole new level.

When it gets to be several degrees below freezing, the metal of the train tracks can contract to the point that it will pull up the bolts holding it in place, or even stress fracture.

Crews will soak long pieces of rope in kerosene and burn it to warm up the tracks, expanding them back into place for repairs. Once the track is warmed, it’ll be re-bolted, or welding repairs can be affected on the broken tracks.

Source: Chicago Is So Ridiculously Cold That the Railroad Tracks Need to Be on Fire to Keep the Trains Moving