Tutorial 0.4 Parameter Passing

Parameter passing

In this tutorial we will go over how to pass a parameter to a view.

Passing a parameter to a view

Having a static hello world page is nice, but it would be better if we could pass a message to our hello world page to display it. To do this, we first need to change our view to accept a message and display it.

Changing our view to accept a message is easy. Open the index.clj file and change the line which looks like:

(defview []

to

(defview [message]

Since views are basically functions, we can simply add a parameter to the function then use it. To add a parameter to a view function, simply add it to the vector when defining the view.

Now that we have a message parameter, we can display it. Change the line:

[:p "Hello World!"]]))

to

[:p (clj-html.helpers/h message)]]))

We assume message is a string, and simply display it as the content of our view. Since the message may be something the user enters, we use the “h” function in clj-html.helpers which sanitizes the message (mainly strips script tags) to avoid a cross site scripting vulnerability. How to avoid website vulnerabilities is outside the scope of this tutorial. However, if you’re displaying text which may have been entered by a user, it’s generally a good idea to sanitize it with the “h” function.

The last thing we need to do is pass a message to our view to display it. This requires us to update our home controller.

In the home_controller.clj file, change the action:

(defn index [request-map]
  (render-view (home-request-map request-map)))

to

(defn index [request-map]
  (render-view (home-request-map request-map) "Hello World! (from controller)"))

If we save both files and reload our page, we should see a message from the controller.

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