Rails 3 Passing a variable from link_to to javascript

Question

If a user is on a form page, I am trying to throw a confirm message if they navigate away without clicking the update button.

The coffeescript code I am using is as follows

# used to detect if a user is navigating off a page
if form_click == true
  window.onbeforeunload = ->
    "You have unsaved data! do you really want to exit?"

If I use if 1 ==1 or 1 ==2 as a test case, it works perfectly fine. However, I am having diffculty in sending a variable from the link_to code to set form_click.

I have tried the following

<%= f.button :button, :class => 'btn-primary',
            data: {form_click: true},
            remote: true %>

But I am not able to pass the variable to the coffeescript code. I am definitely not proficient with javascript and coffeescript, as this probably shows, and would be grateful of any advice on how to resolve this would be much appreciated

roo · Accepted Answer · 2014-08-19 13:18:18Z

1

Have a look at the generated HTML. I suspect that the link_to is creating something similar to:

<button class="btn-primary" data-form_click="true" data-remote="true"></button>

If so then the coffeescript you need to have would be something like:

$('data-form_click').click( ->
  if $(this).attr('data-form_click') == 'true'
    window.onbeforeunload = ->
      confirm("You have unsaved data! Do you really want to exit?")
)

The code above is off the cuff, but the main point is that the attribute on the button is a string, not a boolean, so you need to adjust accordingly.

Use the JS debugging tools to place a breakpoint so you can inspect the value of form_click is also another way to see what you should be comparing to.

answered Aug 19, 2014 at 13:18

roo

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2 Comments

Sylvain Leroux Over a year ago

Very good catch: "the attribute on the button is a string". As == in CoffeeScript test for both value and type (like === in JavaScript) OP should use the string 'true' not the boolean true. BTW, attr() always returns a string, whereas data() try to cast to some other native type (see stackoverflow.com/questions/25321554/…)

roo Over a year ago

Huh - I've never looked at data() in the jQuery docs. You could reduce the condition to if $(this).data('form_click') - looks much nicer

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