Lodash & requiring Partial Libraries

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At the bottom of the table, the user chooses an item and enter how many times they lifted it. I love it! But, management is never satisfied! Nope, they just sent us a new requirement. To inspire people to lift more, they want to auto-fill that box with a random number.

To get that random number, we're going to use a library called Lodash. Well, actually, you can easily get a random number with Math.random()... but using Lodash will be really interesting. Just trust me!

Google for the Lodash library. It's basically a big package of functions. Under Documentation, one of them is _.random().

Ok cool! Let's get this installed. In your terminal, run

yarn add lodash --dev

Next, in RepLogApp.js, on top, add const _ = require('lodash'):

... lines 1 - 7
const _ = require('lodash');
... lines 9 - 215

Go make sure it finished downloading. Perfect!

Find the clearForm() method near the bottom: this is called after we submit the form. Add $form.find() to fetch the reps field, then add .val(_.random(1, 10)):

... lines 1 - 7
const _ = require('lodash');
... lines 9 - 11
class RepLogApp {
... lines 13 - 171
_clearForm() {
... lines 173 - 177
// pre-fill with a random rep number
$form.find('[name="reps"]').val(_.random(1, 10));
... lines 181 - 195
... lines 197 - 215

To make sure that box has a value on load, head up to the constructor and add this._clearForm():

... lines 1 - 11
class RepLogApp {
constructor($wrapper, initialRepLogs) {
... lines 14 - 18
for (let repLog of initialRepLogs) {
... line 20
... lines 23 - 38
... lines 40 - 195
... lines 197 - 215

Perfect! Refresh now! Yes! There's our super random number. And it resets each time we submit. Management is going to love this.

Require only Part of a Library

So why the heck are we really doing this? It wasn't obvious, but the compiled rep_log.js file just got a lot bigger! It's 2.7Mb... but before, it was 1.27! Woh! That's all from lodash! We're importing every function from that library... even though we only need one!

So... question: is there a way for us to import just one thing? Well, it depends on how the library you're using is built. For lodash, it is possible! Look inside node_modules/ for lodash. The library is just a bunch of tiny functions all separated into individual files. When you require lodash, it loads a file that requires all of these. But... we could also require just a single file. In this case, number.js holds what we need... plus a few other things. We could require number.js or random.js.

Back in our code, change to const _ = require('lodash/number'):

... lines 1 - 7
const _ = require('lodash/number');
... lines 9 - 215

In the browser, everything still works. And the package is back down to 1.3Mb!

That's great! And we're now ready to talk about the require function's hipper, better-looking, and younger sibling: import.

Leave a comment!

  • 2018-05-08 weaverryan

    Hey einue!

    No reason really :). Well, actually, I was a bit lazy. It makes senes to use _ when you are importing all of lodash. But, when we import just lodash/number, we should probably give it a different name, like _number or something like that.


  • 2018-05-08 einue

    Is there any reason why you named the constant _ for loadash/number?