Add fill_option to Selenium for clearing with backspaces

Sending the correct number of backspace keys to clear an input before
filling it in with the desired text more accurately mimics real-world
behavior, which can be useful when used with libraries that want to
maintain a tight control over the DOM, such as React.js.

This option can be used by passing `:fill_options` to the `fill_in`
method in your feature specs:

  fill_in 'my_input', :with => 'my text',
    :fill_options => { :clear => :backspace }

Or, with the Ruby 1.9 style syntax:

  fill_in 'my input', with: 'my text'
    fill_options: { clear: :backspace }

History.md

@@ -4,6 +4,7 @@ Release date: unreleased
 ### Added
 
 * 'formmethod' attribute support in RackTest driver [Emilia Andrzejewska]
+* Clear field using backspaces in Selenium driver by using `:fill_options => { :clear => :backspace }` [Joe Lencioni]
 
 #Version 2.4.4
 Release date: 2014-10-13

lib/capybara/selenium/node.rb

@@ -23,7 +23,7 @@ class Capybara::Selenium::Node < Capybara::Driver::Node
     end
   end
 
-  def set(value)
+  def set(value, fill_options)
     tag_name = self.tag_name
     type = self[:type]
     if (Array === value) && !self[:multiple]
@@ -42,9 +42,17 @@ class Capybara::Selenium::Node < Capybara::Driver::Node
       elsif value.to_s.empty?
         native.clear
       else
-        #script can change a readonly element which user input cannot, so dont execute if readonly
-        driver.browser.execute_script "arguments[0].value = ''", native
-        native.send_keys(value.to_s)
+        if fill_options[:clear] == :backspace
+          # Clear field by sending the correct number of backspace keys.
+          backspaces = [:backspace] * self.value.to_s.length
+          native.send_keys(*(backspaces + [value.to_s]))
+        else
+          # Clear field by JavaScript assignment of the value property.
+          # Script can change a readonly element which user input cannot, so
+          # don't execute if readonly.
+          driver.browser.execute_script "arguments[0].value = ''", native
+          native.send_keys(value.to_s)
+        end
       end
     elsif native.attribute('isContentEditable')
       #ensure we are focused on the element

lib/capybara/spec/session/fill_in_spec.rb

@@ -180,4 +180,24 @@ Capybara::SpecHelper.spec "#fill_in" do
       end.to raise_error(Capybara::ElementNotFound)
     end
   end
+
+  context "with { :clear => :backspace } fill_option", :requires => [:js] do
+    it 'should only trigger onchange once' do
+      @session.visit('/with_js')
+      @session.fill_in('with_change_event', :with => 'some value',
+                       :fill_options => { :clear => :backspace })
+      # click outside the field to trigger the change event
+      @session.find(:css, 'body').click
+      expect(@session.find(:css, '.change_event_triggered', :match => :one)).to have_text 'some value'
+    end
+
+    it 'should trigger change when clearing field' do
+      @session.visit('/with_js')
+      @session.fill_in('with_change_event', :with => '',
+                       :fill_options => { :clear => :backspace })
+      # click outside the field to trigger the change event
+      @session.find(:css, 'body').click
+      expect(@session).to have_selector(:css, '.change_event_triggered', :match => :one)
+    end
+  end
 end