Lodash & requiring Partial Libraries
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Login SubscribeAt 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 | |
| } | |
| this._clearForm(); | |
| // ... 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.
Is there any reason why you named the constant _ for loadash/number?