vue

Debounce inside a Vue composable

In the Queerlit frontend, I keep a query object in vuex state, and there’s a helper function for modifying the query object and then immediately performing a search request. This helper lives in a composable, useSearch() in search.composable.js.

The search function is debounced, because it may be issued multiple times, quickly in succession. This happens for instance when using autocomplete. When selecting a suggested term:

Clear the free-text input (update query and search!)
Add the selected term object (update query and search!)

However, the debounced function is created (debounce invoked) inside the composable. When using the composable from different components/composables, they will each generate and use its own debounced function, and the debouncing has no effect. It will do the delay part, there is of course no way for one function to abort earlier invocations of another function.

To make sure that different composable users will use the same object, I had to move the object up to module scope. I couldn’t actually do the debouncing there, though, because the search function depends on other composables. Best practice seems to be to not use composables outside the setup function or other composables.

So this is the structure of my solution:

let debouncedSearch;

export default function useSearch() {
  const { commit } = useStore(); // This is used in doSearch()
  
  async function doSearch() {
    // await an API request
    // commit results to store
  }

  debouncedSearch = debounce(doSearch, 50);
 
  function setQuery(params) {
    // commit query modifications to store
    debouncedSearch();
  }
}

The debounced function is declared outside the composable, in module scope. But it is defined (given its value) inside the composable.

Each usage of the composable will redefine the function (invoke debounce) but then it will update the module-scope variable, so that all users will, in the end, use the same debounced function.

Does this help you? Do you know of another (better) way to use debounce inside a composable?

Streams in Vite

I’m trying to use N3 to parse and query Turtle files in a Vite/Vue 3 project. The N3 readme says “N3.js seamlessly works in browsers via webpack or browserify” and I had trouble interpreting what that would mean in a Vite context. I made an attempt at properly learning all about bundling, but I did some trial and error in parallel, which in the end worked out fine:

First off, I had to add a shim for global in vite.config.js (thanks Richard Oliver Bray):

export default defineConfig({
   // ...
   define: {
     global: {},
   },
 });

Then I got problems when using N3.Store.match:

Uncaught TypeError: Cannot read properties of undefined (reading ‘call’)

The culprit was a line saying Stream.call(this), i.e. Stream is what’s undefined. Here’s where I got lost installing and aliasing various browserified forks, before I just did:

yarn add events

and voilà!

N3 uses the Node.js Stream class. In a browser environment, it instead uses EventEmitter from the events library. So we just had to get that in place.

Comma, comma & and

I recently had to concatenate author names with commas and an ampersand in the following manner:

commaAnd(['Emir Jong']);
// becomes: "Emir Jong"

commaAnd(['Kristian Josefsen', 'Tetyana Bohuňková']);
// becomes: "Kristian Josefsen & Tetyana Bohuňková"

commaAnd(['Luana Ferreira Carvalho', 'Jian Tu', 'Ambessa Afwerki']);
// becomes: "Luana Ferreira Carvalho, Jian Tu & Ambessa Afwerki"

Here are a few implementations in JavaScript:

function commaAnd(strs, comma = ", ", and = " & ") {
  const glue = (i) => ["", and, comma][Math.min(strs.length - i - 1, 2)];
  return strs.reduce((res, str, i) => res + str + glue(i), "");
}

function commaAnd(strs, comma = ", ", and = " & ") {
  return (
    ((s) => (s ? s + and : ""))(strs.slice(0, -1).join(comma)) + strs.slice(-1)
  );
}

function commaAnd(strs, comma = ", ", and = " & ") {
  const init = strs.slice(0, -1).join(comma);
  return [init, strs.slice(-1)].filter((s) => s).join(and);
}

But then each author name needed a bit of markup as well. In Vue, we could concatenate HTML strings and use v-html, but we should avoid that if we can.

Here’s my method using slot scopes (much like that todo list example):

<template>
  <span>
    <span v-for="(item, i) in items" :key="i"
      ><slot name="item" :item="item">{{ item }}</slot
      >{{ [null, and, comma][Math.min(items.length - i - 1, 2)] }}</span
    >
  </span>
</template>

<script>
export default {
  name: "CommaAnd",
  props: {
    items: { type: Array, default: Array },
    comma: { type: String, default: () => ", " },
    and: { type: String, default: () => " & " },
  },
};
</script>

The usage is as follows:

<CommaAnd :items="authors">
  <template v-slot:item="{ item }">
    {{ fullName(item)
    }}<sup>{{
      affiliations.indexOf(item.affiliation) + 1
    }}</sup></template
  >
</CommaAnd>

From the CommaAnd component, we call out to the parent component to define how to render each item. Inside the component, we only define what to do in between the items.

Note that much of the whitespace between elements and interpolations ({{ }}) must be eliminated when we are dealing with inline text. Furthermore, forcing HTML/XML into short lines is difficult (Prettier is doings its best here…) and the Vue syntax for slot scopes is a bit entangled, so the result is not super readable.

The resulting output is also pretty loud. Lots of <span>s in <span>s. If you don’t want that you should probably go with v-html anyway.

Push to deploy Vue app

With this workflow, my web space contains a git remote which, whenever pushed to, builds the Vue project and puts it on a public path.

A few years ago I, working with Drupal 8, I was using Pantheon and I really enjoyed the workflow, where deploying comprised of simply git push‘ing to a certain remote. (I think maybe this model was made popular by Heroku?)

Nowadays I’m getting into JS development. A framework that I have been using recently is Vue. One of my current project ideas is using Vue to develop a small web app for crawling some websites and grabbing data on arbitrary movies. I want to do the development in short iterations, and I want it to be easy to publish each step of progress.

So today I set up a push-to-deploy workflow for my Vue app. I don’t want to give the prototype its own domain name, so I’m publishing it in a subdirectory: klavaro.se/filminfo

Workflow

With this workflow, my web space contains a git remote which, whenever pushed to, builds the Vue project and puts it on a public path.

The deploy procedure is reduced to a single command: git push deploy

Git setup on server

The web host I am using is NearlyFreeSpeech.net, which provides SSH access and git.

SSH into the server and create the remote repository:

cd /home/private
git init --bare /home/private/myproject.deploy

Clone it to get the local git repository:

git clone myproject.deploy myproject.checkout

Then add a post-receive hook script in the remote repository:

touch myproject.deploy/hooks/post-receive
chmod +x $_
# Bonus trick: That $_ expands to the last argument in the previous command, in this case the path of the new file.

Edit the script as follows (making changes where appropriate, depending on your Vue setup):

!/bin/bash
# -e exits as soon as any command fails
# -x prints each command being executed
set -ex
CHECKOUT=/home/private/myproject.checkout
SITE=/home/public/myproject
cd $CHECKOUT
git --git-dir .git fetch
git --git-dir .git reset --hard origin/master
yarn install --production
yarn build --dest $SITE

Local git configuration

Back on your local machine, all you have to do is add the new remote:

git remote add deploy user@example.com:/home/private/myproject.deploy

Give it a spin:

echo Hello World! > hello.txt
git add hello.txt
git commit -m 'Deploy test'
git push deploy
# Verify that the post-receive script output is showing.
# Clean up after yourself:
git reset --hard HEAD^
git push -f deploy

Configure Vue for a subdirectory

Vue is normally configured to serve the app at the root level of the host. I want to serve it at the root level locally, but in a subdirectory on the web server. I accomplished this using environment variables.

Locally, create .env containing:

PUBLIC_PATH=/

Edit vue.config.js like this:

module.exports = {
  publicPath: process.env.PUBLIC_PATH,
}

If you use vue-router, configure it (in main.ts):

const router = new VueRouter({
  base: process.env.PUBLIC_PATH,
  // ...
})

Finally, in the local repository on the server (that’s an oxymoron, but you know what I mean), create .env.local, containing:

PUBLIC_PATH=/myproject

After that, commit and push the changes you made on your local machine.