Cannot access Rails variable inside Javascript tag

Question

All the other solutions in stackoverflow doesn't seem to work for me so i'm posting my code for assistance. I want to output the variable: @less_per_unit via jquery

Here is my tag inside _form.html.erb:

<script>
$(document).on('keyup', ".input-quantity", function(){ 
  $.ajax({
      url:  "/so_check_increment",
      type: "GET",
      data: { quantity: $(this).val(), product_id: $(this).closest('tr').find('.input-product_code').val()}
  }); 
    $(this).closest('td').next('td').find('.increment').text('<%== j @less_per_unit%>');
}); 
</script>

And here is my controller:

  def check_increment
    @less_per_unit = "testing"
  end

I know that the ajax works, i've also set up the routes. If I try binding.pry, I know that rails can find @less_per_unit, but I can't output it with javascript.

Aakash Gupta · Accepted Answer · 2017-11-13 04:45:23Z

1

This is not working because:

Let us say this form is rendered in action 'new' of controller 'Post', then @less_per_unit needs to be initialised there to use it in the view file of that action which you are using. Where as you are using an AJAX call and during that call, you are defining an instance variable which will definitely be not accessible to the already rendered html file.

So, you need to return JSON data from your check_increment action and receive that data in AJAX call response and then use it.

edited Nov 13, 2017 at 4:45

answered Nov 12, 2017 at 19:22

Aakash Gupta

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15 Comments

Bassman Over a year ago

Actually j is rails code for “escape javascript”. I learned that from the other stack overflow questions similar to mine. I tried removing the extra = and j but it still doesnt work.

Aakash Gupta Over a year ago

Okay. I didn't know that. But why an extra '='. As per documentation, <%= j @less_per_unit %> should work fine.

Bassman Over a year ago

I tried that and it still doesn't show any value. I tried console.log('<%= j @less_per_unit %>') also. No luck.

Aakash Gupta Over a year ago

Isn't it obvious that this will not work? The reason is: Let us say this form is rendered in action 'new' of controller 'xyz', then @less_per_unit needs to be initialised there to use it in the view file of that action which you are using. Where as you are using an AJAX call and during that call, you are defining an instance variable which will definitely be not accessible to the already rendered html file.

Aakash Gupta Over a year ago

So, have you basically understood why your code was not working earlier? I hope you have read the explanation.

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