Building Blocks: Context, Action and Pipe

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This lesson aims to introduce the core items that make an Autopilot Script. Let's shape your mental model together!

Data model (element-value tuple)

Autopilot connects the elements on a web page with the data. As far as Autopilot is concerned, the data's nature is a tuple of an element (a DOM node) and a value (string, number, object or boolean). A pipe can modify one side of the tuple at a time. The defaults are the entire #document for an element and an empty object {} for a value.

Pipe

A pipe is a sole-purpose mini-program that modifies the data according to the pipe's type. It keeps a connection with the page, so you get feedback instantly whenever you look at the pipe. Here are a few most common pipe groups: List, Value, DOM, Object, Boolean.

Pipes can form a chain – a pipeline. The output of one pipe is the input for the following item. This way, a series of modifications apply to the data on its way to the action.

Consider this pipeline example:

DOM.queryOne pipe uses a CSS selector to replace the initial element (#document) with the input[type="text"] node.
The following Value.getConstant pipe replaces the default value ({}) with a constant – some text you specify.
As a result, the "input" action receives the tuple that provides both an input page element to interact and some text to enter there.

Action

Action changes the state of things. Action's type defines what sort of effect happens. In contrast to pipes, you need to execute an action to see its impact. The two most common action groups are Page and Flow.

The "input" action mentioned above will consume the element-value tuple and act by entering the "value" into the "element".

Context

A context is a set of instructions on how to recognise the page and what to do with it.

Matchers, a particular type of actions, facilitate context recognition by describing a page's desired state. The only context with no matchers is the <main> one – it doesn't need to match anything, as this is where the Script starts.

When all the matchers of a context give a green light, the control goes to the rest of the context's actions. Learn more about how this works in the context matching lesson.