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Rails 6 + UJS: make ajax call on blur without jQuery


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I have a form with two input text fields. The datalist for the second field needs to be populated when the first field has a value. I have everything working as I want except I can't work out how to fire the ajax call when the first field loses focus (I have put in a link I can click to test everything else is working.)


class Org < ApplicationRecord
has_many: competitions


= f.label "Competition:"
= text_field_tag :eek:rg, @match.org&.name, list: "orgs", size: 60 # onblur: ?
= text_field_tag :competition, @match.competition&.name, list: "comps", size: 30

= options_for_select Org.all.map(&:name).sort

= render "comps"


= options_for_select @comps.map(&:name).sort


def comps
org = Org.find_from_identifier(params[:eek:rg])
@comps = org&.competitions || []
respond_to do |format|


comps = document.getElementById("comps")
comps.innerHTML = "<%= j render "comps" %>"

If I put this line into the form everything works as I expect when I click it:

= link_to 'test', update_comps_path(org: 'scottishfootballleague'), remote: true

(Routes.rb has get 'matches/comps', to: "matches#comps", as: :update_comps in it.)

So my question is how do I do what that link does when the first input field loses focus?

I tried putting onblur: 'updateComps()' into the field and using

function updateComps() {
var org = document.getElementById("org").value
fetch("/matches/comps?org=" + org )

This works in the sense that the call gets made at the right time but I'm missing whatever magic data-remote: true attaches to the link to make it an ajax call that works in the rails world. Am I missing a Rails helper? Or do I need to instruct fetch() with what to do with the js that gets returned?

Edit: I've got as far as working out that the response to the fetch consists of the javascript I expect, and which presumably needs to be executed. I've tried this:

function updateComps() {
var org = document.getElementById("org").value
fetch("/matches/comps?org=" + org,
{ credentials: "include" })
.then(response => {

There are two problems with this. 1) it doesn't work 2) this doesn't seem very rails-like.

Update (with an answer)

I got the fetch approach working and executing the server generated js:

function updateComps() {
var org = document.getElementById("org").value
fetch("/matches/comps.js?org=" + org,
{ credentials: "include" })
.then(response => response.text())
.then(text => {

I'm still not at all sure what the "Rails way" of doing this is. Rails.ajax() seems to have been removed (or is only available 'internally') according to some github discussions.

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