jdsutherland

jdsutherland

Modern Front-End Development for Rails: B7 pg 164 server JSON ids are numbers causing javascript Array#includes to always return false

After completing the section Using Data in Stimulus (ends pg 167), I noticed something wrong with Ajax updates. After running the rake task to sell out concerts, things looked fine on initial browser load:


but after Ajax it would change from “Sold Out” to “0 Tickets Remaining”:

The data attributes looked like this:
image

So concertSoldOutValue was suspiciously being set to false. The issue is that Array#includes is called with a string on an array of numbers (always false):

      concertElement.dataset.concertSoldOutValue = soldOutConcertIds.includes(
        concertElement.dataset.concertIdValue
      )
typeof soldOutConcertIds[0]:  number

The ids coming from the server JSON are numbers. One solution is to convert the ids to a string:

class SoldOutConcertsController < ApplicationController
  def show
    concerts = Concert.includes(:venue, gigs: :band).all
    sold_out_concert_ids = concerts
      .select(&:sold_out?)
      .map(&:id)
      .map(&:to_s)
    render(json: {sold_out_concert_ids: sold_out_concert_ids})
  end
end

Perhaps TypeScript could be leveraged to prevent this kind of bug?

First Post!

noelrappin

noelrappin

Author of Modern Front-End Development for Rails

This is a really great catch, I’ll fix it in the next update.

Where Next?

Popular Pragmatic Bookshelf topics Top

johnp
Running the examples in chapter 5 c under pytest 5.4.1 causes an AttributeError: ‘module’ object has no attribute ‘config’. In particula...
New
belgoros
Following the steps described in Chapter 6 of the book, I’m stuck with running the migration as described on page 84: bundle exec sequel...
New
jamis
The following is cross-posted from the original Ray Tracer Challenge forum, from a post by garfieldnate. I’m cross-posting it so that the...
New
rmurray10127
Title: Intuitive Python: docker run… denied error (page 2) Attempted to run the docker command in both CLI and Powershell PS C:\Users\r...
New
adamwoolhether
When trying to generate the protobuf .go file, I receive this error: Unknown flag: --go_opt libprotoc 3.12.3 MacOS 11.3.1 Googling ...
New
AndyDavis3416
@noelrappin Running the webpack dev server, I receive the following warning: ERROR in tsconfig.json TS18003: No inputs were found in c...
New
brunogirin
When trying to run tox in parallel as explained on page 151, I got the following error: tox: error: argument -p/–parallel: expected one...
New
dsmith42
Hey there, I’m enjoying this book and have learned a few things alredayd. However, in Chapter 4 I believe we are meant to see the “&gt;...
New
dtonhofer
@parrt In the context of Chapter 4.3, the grammar Java.g4, meant to parse Java 6 compilation units, no longer passes ANTLR (currently 4....
New
dachristenson
I just bought this book to learn about Android development, and I’m already running into a major issue in Ch. 1, p. 20: “Update activity...
New

Other popular topics Top

Devtalk
Hello Devtalk World! Please let us know a little about who you are and where you’re from :nerd_face:
New
AstonJ
What chair do you have while working… and why? Is there a ‘best’ type of chair or working position for developers?
New
AstonJ
Or looking forward to? :nerd_face:
492 13311 267
New
New
PragmaticBookshelf
Build highly interactive applications without ever leaving Elixir, the way the experts do. Let LiveView take care of performance, scalabi...
New
rustkas
Intensively researching Erlang books and additional resources on it, I have found that the topic of using Regular Expressions is either c...
New
hilfordjames
There appears to have been an update that has changed the terminology for what has previously been known as the Taskbar Overflow - this h...
New
PragmaticBookshelf
Author Spotlight: Peter Ullrich @PJUllrich Data is at the core of every business, but it is useless if nobody can access and analyze ...
New
AstonJ
This is cool! DEEPSEEK-V3 ON M4 MAC: BLAZING FAST INFERENCE ON APPLE SILICON We just witnessed something incredible: the largest open-s...
New
Fl4m3Ph03n1x
Background Lately I am in a quest to find a good quality TTS ai generation tool to run locally in order to create audio for some videos I...
New

Sub Categories: