Skip to content

<mvt:eval>#

The <mvt:eval> tag in Miva Merchant’s template language is used to execute an expression and output its value directly to the page. It functions similarly to <mvt:assign> but does not store the value in a variable—instead, it writes the result immediately to the template’s output.

This makes <mvt:eval> a simple and efficient way to display calculated or dynamic content directly within your templates.

Empresa Requirement

Requires Miva Empresa Engine 5.18 or higher.

Syntax#

<mvt:eval expr="expression, string, or number" />

Attributes#

Attribute Description
expr The expression to evaluate, which can include strings, numbers, variables, or functions.

Examples#

Basic Arithmetic#

Perform arithmetic operations directly in the expression.

The sum is: <mvt:eval expr="1 + 2" />

Output: 

The sum is: 3

Outputting Strings#

Display a string value directly on the page.

<mvt:eval expr="'Hello, Miva!'" />

Output: 

Hello, Miva!

Using Numbers#

Perform calculations with numeric values.

<mvt:eval expr="(10 + 5) * 2" />

Output: 

30

Using Expressions#

Execute complex expressions or functions supported by the Miva Empresa engine.

<mvt:assign name="l.myvariable" value="'Hello World'" />
<mvt:eval expr="substring(l.myvariable, 2, len(l.myvariable))" />

Output: 

ello World

Concatenation#

Combine strings and calculated values using the $ concatenation operator.

<mvt:eval expr="'The length of this string is: ' $ len('example text')" />

Output: 

The length of this string is: 12

Best Practices#

  1. Keep Expressions Simple:

    • Avoid overly complex expressions in <mvt:eval>. Use separate <mvt:assign> statements for clarity when needed.

  2. Combine with Functions:

    • Use Miva functions like substring, len, or mathematical operations for dynamic content generation.

  3. Use Concatenation Wisely:

    • The $ operator is powerful but can become difficult to read in complex expressions. Break down concatenations if necessary.

  4. Comment Your Code:

    • For advanced expressions, include comments to explain their purpose for better maintainability.

Advanced Example: Dynamic Output with Calculations#

This example combines multiple operations to display dynamic content.

<mvt:assign name="g.base_price" value="50" />
<mvt:assign name="g.discount" value="10" />
<mvt:assign name="g.final_price" value="g.base_price - g.discount" />

<p>Base Price: $<mvt:eval expr="g.base_price" /></p>
<p>Discount: $<mvt:eval expr="g.discount" /></p>
<p>Final Price: $<mvt:eval expr="g.final_price" /></p>

Output: 

Base Price: $50
Discount: $10
Final Price: $40

Summary#

The <mvt:eval> tag is a versatile tool for directly outputting calculated or dynamic content in Miva templates. By combining strings, numbers, variables, and functions, <mvt:eval> allows you to create highly dynamic and interactive e-commerce pages.

Key Points:#

  • Use <mvt:eval> to directly output the result of expressions.
  • Combine with Miva functions and operators for powerful dynamic content generation.
  • Avoid excessive complexity in single expressions for better readability and maintainability.