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Using VDL Expressions

Expressions are statements used to insert dynamic content into a VDL page or programmatically control layout and data flow.
They are specified as attributes of VDL components - we examined a simple expression in the earlier section Creating a First VDL View. 
<p vdl-text="=scenario.entities.Return.value"></p>
An expression is denoted by an equals sign = at the start of an attribute value. Everything after the equals sign is evaluated and re-evaluated when any referenced entities change.

Not all VDL attributes accept expressions. The VDL Reference enumerates all of the available standalone attributes and attributes within VDL tags. The accepts expression flag indicates when attributes accept expressions.

Covered Topics
  • VDL Expression Language Syntax
    There are several basic rules for the VDL expression language.
  • View Global Scope
    Several objects are implicitly within scope in views and available to expressions
  • Accessing Entities and Other Model Data
    When you reference a scalar entity or set/array element from the model, an object with two properties is returned.
  • Using Dynamic Variables
    Dynamic variables allow you to define calculations or operations once and reference them in multiple expressions.
  • Using Loops with Arrays and Sets
    VDL provides a means of repeating a block of VDL content and looping around each element in an array or set..
  • Working with Conditional VDL Attributes
    You can implement conditional logic by combining expressions with one of a number of conditional VDL attributes. This is generally used to control whether content is included in the page or not, whether it is hidden, or how it is styled.
  • Using VDL Includes
    When an app written with VDL becomes large, it is common to require the same functionality in several independent views. There is also a case for creating custom extensions to handle certain features or layouts across multiple views. Both requirements are satisfied with the element.
  • Advanced Expressions
    In addition to accessing the available global objects, you can make use of any standard JavaScript syntax and globals provided by the insight API, such as insight, lodash _ and jquery $.
Parent Topic Using VDL to Create Custom Views