Rails: Open link in new tab (with 'link_to')

I have this code:

<%= link_to image_tag("facebook.png", :class => "facebook_icon", :alt => "Facebook", :target => "_blank"),                 
            "http://www.facebook.com/mypage" %>

How can I make it open in a new tab when a user clicks the link?

The target: :_blank parameter should be a parameter of link_to, whereas you put it in image_tag parameters. Modify your code like this:

<%= link_to image_tag("facebook.png", class: :facebook_icon, alt: "Facebook"), "http://www.facebook.com/mypage", target: :_blank %>

Or with a block:

<%= link_to "http://www.facebook.com/mypage", target: :_blank do %>
  <%= image_tag("facebook.png", class: :facebook_icon, alt: "Facebook") %>     
<% end %>  

Try this:

<%= link_to image_tag("facebook.png", :class => "facebook_icon", :alt => "Facebook"), "http://www.facebook.com/mypage", :target => "_blank" %>

You can also use target: :_blank instead of target: '_blank'

<%= link_to image_tag("facebook.png", class: "facebook_icon", alt: "Facebook"), "http://www.facebook.com/mypage", target: :_blank %>

link_to do

<%= link_to "http://www.facebook.com/mypage", target: :_blank do %>
  <%= image_tag "facebook.png", class: "facebook_icon", alt: "Facebook" %>
<% end %>

If you're looking for how to open a link in a new tab within html (for anyone came here from Google), here:

<a href="http://www.facebook.com/mypage" target="_blank">Link name</a>