expressions.md

Expressions

• Overview
• Expressions API
  • expression.expr
  • expression.eval(model)
  • expression.safeEval(model)
  • expression.identifiers()

Overview

The text we put inside directive's values are called binding expressions. In d3-view, a binding expression consists of a single JavaScript expression but not operations. The difference between expressions and operations is akin to the difference between a cell in an Excel spreadsheet vs. a proper JavaScript program.

Valid expression are:

"The sun"               //  literal
theme                   //  An identifier (a property of a model)
dosomething()           //  A function
[theme, number]         //  Arrays of identifiers
x ? "Hi" : "goodbye"    //  Conditionals

and complex combinations of the above

user.groups().join(", ")
[theme, user.groups(), "Hi"]

The original implementation of the expression API was taken from jsep.

Expressions API

Expression can be created via the javascript API:

var expression = viewExpression(<expression string>);

expression.expr

The original expression string passed to the Expression constructor.

expression.eval(model)

Evaluate an expression with data from a given model. The model can be a [model][] instance or a vanilla object.

expression.safeEval(model)

Same as expression.eval but does not throw an exception if evalutation fails. Instead it logs the error end returns nothing.

expression.identifiers()

Array of identifiers (model properties) in the expression.