agadoo

Ag-a-doo-doo-doo, push pineapple, shake the tree

What this does

Tells you whether the JavaScript library you're building is tree-shakeable.

What it doesn't do

Tell you why tree-shaking fails, if it does. Maybe in a future version.

Hold up — tree what now?

With the advent of JavaScript modules (import and export), it's possible to build libraries that are tree-shakeable. This means that a user of your library can import just the bits they need, without burdening their users with all the code you're not using.

For example, the eases-jsnext library contains a grab-bag of Robert Penner's easing equations, presented as a JavaScript module. I can use it like this in my code...

``js
import * as eases from 'eases-jsnext';

for (let t = 0; t <= 1; t += 0.05) {
const eased = eases.cubicInOut(t)
const str = repeat('', eased 20);
console.log(str);
}

function repeat(str, num) {
let result = '';
num = Math.round(num);
while (num--) result += str;
return result;
}
`

...and all the easing functions that I haven't used will get removed during bundling, if I'm using a modern bundler such as Rollup, webpack or Parcel. Here's what that bundle would look like with Rollup:

`js
'use strict';

function cubicInOut(t) {
return t < 0.5
? 4.0 t t * t
: 0.5 Math.pow(2.0 t - 2.0, 3.0) + 1.0
}

for (let t = 0; t <= 1; t += 0.05) {
const eased = cubicInOut(t);
const str = repeat('', eased 20);
console.log(str);
}

function repeat(str, num) {
let result = '';
num = Math.round(num);
while (num--) result += str;
return result;
}
`

...and here's the result of running it:

`

*
*
**
*
*
*

*
*
*
**
*
*



`

But I digress. The point is that this works because eases-jsnext is a tree-shakeable library.

Using agadoo

Inside your project folder, run Agadoo like so:

`bash
npx agadoo
`

You can install it as a development dependency and run it each time you npm publish — if tree-shaking fails, publishing will be aborted:

`bash
npm install -D agadoo
`

`js
// package.json
{
"scripts": {
"prepublishOnly": "agadoo"
}
}
`

You can specify the module if necessary:

`bash
agadoo dist/my-library.js
``

Help! My library isn't tree-shakeable and I'm not sure why

Firstly, make sure you're exposing a JavaScript module using the "module" field of your package.json (aka pkg.module).

If tree-shaking still fails, it's because Rollup thinks that there are side-effects somewhere in your code. Follow these guidelines:

* Avoid transpilers like Babel and Bublé (and if you're using TypeScript, target a modern version of JavaScript)
* Export plain functions
* Don't create instances of things on initial evaluation — instantiate lazily, when the functions you export are called

License

LIL.