Rails 5/6：如何在 webpacker 中包含 JS 函数？

Question

I am trying to update a Rails 3 app to Rails 6 and I have problems with the now default webpacker since my Javascript functions are not accessible.

I get: ReferenceError: Can't find variable: functionName for all js function triggers.

What I did is:

• create an app_directory in /app/javascript
• copied my development javascript file into the app_directory and renamed it to index.js
• added console.log('Hello World from Webpacker'); to index.js
• added import "app_directory"; to /app/javascript/packs/application.js

• added to /config/initializers/content_security_policy.rb:

   Rails.application.config.content_security_policy do |policy| policy.connect_src :self, :https, "http://localhost:3035", "ws://localhost:3035" if Rails.env.development? end

I get 'Hello World from Webpacker' logged to console, but when trying to access a simple JS function through <div id="x" onclick="functionX()"></div> in the browser I get the reference error.

I understand that the asset pipeline has been substituted by webpacker, which should be great for including modules, but how should I include simple JS functions? What am I missing?

Thanks in advance?

Answer 1

For instructions on moving from the old asset pipeline to the new webpacker way of doing things, you can see here:

https://www.calleerlandsson.com/replacing-sprockets-with-webpacker-for-javascript-in-rails-5-2/

This is a howto for moving from the asset pipeline to webpacker in Rails 5.2, and it gives you an idea of how things are different in Rails 6 now that webpacker is the default for javascript. In particular:

Now it's time to move all of your application JavaScript code from app/assets/javascripts/ to app/javascript/.

To include them in the JavaScript pack, make sure to require them in app/javascript/pack/application.js:

 require('your_js_file')

So, create a file in app/javascript/hello.js like this:

console.log("Hello from hello.js");

Then, in app/javascript/packs/application.js , add this line:

require("hello")

(note that the extension isn't needed)

Now, you can load up a page with the browser console open and see the "Hello!" message in the console. Just add whatever you need in the app/javascript directory, or better yet create subdirectories to keep your code organized.

---

More information:

This question is cursed. The formerly accepted answer is not just wrong but grotesquely wrong, and the most upvoted answer is still missing the mark by a country mile.

anode84 above is still trying to do things the old way, and webpacker will get in your way if you try that. You have to completely change the way you do javascript and think about javascript when you move to webpacker. There is no "scoping issue". When you put code in a web pack it's self-contained and you use import/export to share code between files. Nothing is global by default.

I get why this is frustrating. You're probably like me, and accustomed to declaring a function in a javascript file and then calling it in your HTML file. Or just throwing some javascript at the end of your HTML file. I have been doing web programming since 1994 (not a typo), so I've seen everything evolve multiple times. Javascript has evolved. You have to learn the new way of doing things.

If you want to add an action to a form or whatever, you can create a file in app/javascript that does what you want. To get data to it, you can use data attributes, hidden fields, etc. If the field doesn't exist, then the code doesn't run.

Here's an example that you might find useful. I use this for showing a popup if a form has a Google reCAPTCHA and the user hasn't checked the box at the time of form submission:

// For any form, on submit find out if there's a recaptcha
// field on the form, and if so, make sure the recaptcha
// was completed before submission.
document.addEventListener("turbolinks:load", function() {
  document.querySelectorAll('form').forEach(function(form) {
    form.addEventListener('submit', function(event) {
      const response_field = document.getElementById('g-recaptcha-response');
      // This ensures that the response field is part of the form
      if (response_field && form.compareDocumentPosition(response_field) & 16) {
        if (response_field.value == '') {
          alert("Please verify that you are not a robot.");
          event.preventDefault();
          event.stopPropagation();
          return false;
        }
      }
    });
  });
});

Note that this is self-contained. It does not rely on any other modules and nothing else relies on it. You simply require it in your pack(s) and it will watch all form submissions.

Here's one more example of loading a google map with a geojson overlay when the page is loaded:

document.addEventListener("turbolinks:load", function() {
  document.querySelectorAll('.shuttle-route-version-map').forEach(function(map_div) {
    let shuttle_route_version_id = map_div.dataset.shuttleRouteVersionId;
    let geojson_field = document.querySelector(`input[type=hidden][name="geojson[${shuttle_route_version_id}]"]`);

    var map = null;

    let center = {lat: 36.1638726, lng: -86.7742864};
    map = new google.maps.Map(map_div, {
      zoom: 15.18,
      center: center
    });

    map.data.addGeoJson(JSON.parse(geojson_field.value));

    var bounds = new google.maps.LatLngBounds();
    map.data.forEach(function(data_feature) {
      let geom = data_feature.getGeometry();
      geom.forEachLatLng(function(latlng) {
        bounds.extend(latlng);
      });
    });
    map.setCenter(bounds.getCenter());
    map.fitBounds(bounds); 
  });
});

When the page loads, I look for divs with the class "shuttle-route-version-map". For each one that I find, the data attribute "shuttleRouteVersionId" (data-shuttle-route-version-id) contains the ID of the route. I have stored the geojson in a hidden field that can be easily queried given that ID, and I then initialize the map, add the geojson, and then set the map center and bounds based on that data. Again, it's self-contained except for the Google Maps functionality.

You can also learn how to use import/export to share code, and that's really powerful.

So, one more that shows how to use import/export. Here's a simple piece of code that sets up a "watcher" to watch your location:

var driver_position_watch_id = null;

export const watch_position = function(logging_callback) {
  var last_timestamp = null;

  function success(pos) {
    if (pos.timestamp != last_timestamp) {
      logging_callback(pos);
    }
    last_timestamp = pos.timestamp;
  }

  function error(err) {
    console.log('Error: ' + err.code + ': ' + err.message);
    if (err.code == 3) {
      // timeout, let's try again in a second
      setTimeout(start_watching, 1000);
    }
  }

  let options = {
    enableHighAccuracy: true,
    timeout: 15000, 
    maximumAge: 14500
  };

  function start_watching() {
    if (driver_position_watch_id) stop_watching_position();
    driver_position_watch_id = navigator.geolocation.watchPosition(success, error, options);
    console.log("Start watching location updates: " + driver_position_watch_id);  
  }

  start_watching();
}

export const stop_watching_position = function() {
  if (driver_position_watch_id) {
    console.log("Stopped watching location updates: " + driver_position_watch_id);
    navigator.geolocation.clearWatch(driver_position_watch_id);
    driver_position_watch_id = null;
  }
}

That exports two functions: "watch_position" and "stop_watching_position". To use it, you import those functions in another file.

import { watch_position, stop_watching_position } from 'watch_location';

document.addEventListener("turbolinks:load", function() {
  let lat_input = document.getElementById('driver_location_check_latitude');
  let long_input = document.getElementById('driver_location_check_longitude');

  if (lat_input && long_input) {
    watch_position(function(pos) {
      lat_input.value = pos.coords.latitude;
      long_input.value = pos.coords.longitude;
    });
  }
});

When the page loads, we look for fields called "driver_location_check_latitude" and "driver_location_check_longitude". If they exist, we set up a watcher with a callback, and the callback fills in those fields with the latitude and longitude when they change. This is how to share code between modules.

So, again, this is a very different way of doing things. Your code is cleaner and more predictable when modularized and organized properly.

This is the future, so fighting it (and setting "window.function_name" is fighting it) will get you nowhere.

Answer 2

Looking at how webpacker "packs" js files and functions:

/***/ "./app/javascript/dashboard/project.js":
/*! no static exports found */
/***/ (function(module, exports) {

  function myFunction() {...}

So webpacker stores these functions within another function, making them inaccessible. Not sure why that is, or how to work around it properly.

There IS a workaround, though. You can:

1) change the function signatures from:

function myFunction() { ... }

to:

window.myFunction = function() { ... }

2) keep the function signatures as is, but you would still need to add a reference to them as shown here : window.myFunction = myFunction

This will make your functions globally accessible from the "window" object.

Answer 3

Replace the code in your custom java Script file from

function function_name() {// body //}

to

window.function_name = function() {// body //}

Answer 4

From the official rails app guide:

Where to Stick Your JavaScript

Whether you use the Rails asset pipeline or add a tag directly to a view, you have to make a choice about where to put any local JavaScript file.

We have a choice of three locations for a local JavaScript file:

The app/assets/javascripts folder,the lib/assets/javascripts folder and the vendor/assets/javascripts folder

Here are guidelines for selecting a location for your scripts:

Use app/assets/javascripts for JavaScript you create for your application.

Use lib/assets/javascripts for scripts that are shared by many applications (but use a gem if you can).

Use vendor/assets/javascripts for copies of jQuery plugins, etc., from other developers. In the simplest case, when all your JavaScript files are in the app/assets/javascripts folder, there's nothing more you need to do.

Add JavaScript files anywhere else and you will need to understand how to modify a manifest file.

More reading: http://railsapps.github.io/rails-javascript-include-external.html