How do i check if a variable exist, in eex?

EDIT Prior to Phoenix 0.14.0 @company would return nil if it was not set. It was changed to raise so that the assignment would be explicit (explicit over implicit.)

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If you use either @company or assigns.company then an error will be raised. However if you use assigns[:company] then it will return nil if the value is not set.

<%= if assigns[:company] do %>
  <%= Logo.url({@company.logo, @company}, :thumb) %>
<% end %>

It is worth noting that if you are using a nested template then you will need to pass this through too:

<h1>New thing</h1>
<%= render "form.html", changeset: @changeset,
                        action: thing_path(@conn, :create),
                        company: assigns[:company] %>

The selected answer doesn't work.

Try with this :

<%= if Map.has_key?(assigns, :company) do %>
  <%= Logo.url({@company.logo, @company}, :thumb) %>
<% end %>