According to RFC8259:

JSON can represent four primitive types (strings, numbers, booleans, and null) and two structured types (objects and arrays).

Now, with this gem, you can have the 7th one, function.

So, basically, what I'm saying is the json is no longer conform with the RFC8259. The resulting function is not guaranteed to be executable in JavaScript because it doesn't check what's inside the function. It also cannot be parsed back into hash. So, use it at your own risk!

Installation

Add this line to your application's Gemfile:

gem 'functionable-json'

And then execute:

$ bundle

Usage

{
  speed: function(val) {
           return '$' + parseFloat(val).toLocaleString();
         }
}.to_json
#=> "{\"speed\":function(val) { return '$' + parseFloat(val).toLocaleString(); }}"

But, don't go wild just yet because there are limitations:

• You cannot use if keyword because the way JavaScript uses it is different from ruby. It is meant to be used for a simple function. One use case I'm targetting is for formatting options to be used by JavaScript libraries.
• Also, don't put multiple functions on the same line. You'll get unexpected result if you do.
• You should end statement with ;.

If you try the above example on your REPL (e.g. irb or pry) it won't work since the gem will try to find the file that stores the code. So, you need to put it on a file and run it.

How can a JavaScript function be called from Ruby?

Well, technically, it's not a JavaScript function. It's a Ruby method named function that's available in any object. In JavaScript, a form like that is a function declaration, but in Ruby it's a method invocation. So, in that case, val needs to already exist before you call it, and it is. Both function and val are already a method of an object. If you want to use arguments with another name, you need to declare them as variable first.

arg1, arg2 = nil
{
  equality: function(arg1, arg2) {
              return arg1 + ' == ' + arg2
            }
}.to_json
#=> "{\"equality\":function(arg1, arg2) { return arg1 + ' == ' + arg2 }}"

Use Case

One example use case is ApexCharts.RB formatter. You can add tooltip formatter like this:

<%= line_chart data, tooltip: {y: {formatter: function(val) { return '$' + parseFloat(val).toLocaleString(); }}} %>

License

The gem is available as open source under the terms of the MIT License.