How Can I Debug Calculated Values in CSS `calc()` Expressions?

How to Debug CSS Calc() Value

Problem Statement:

I have complex CSS calc() formulas, but it's difficult to debug their calculated values. Is there a way to validate and display these values for debugging purposes?

Answer:

Validating Formulas:

• Check for any errors in the formula syntax, ensuring proper usage of operators and white space.
• Refer to the CSS Values specification for the allowed types and restrictions in calculations.

Debugging Calculated Value:

• Output the calculated value using a pseudo-element (as in your example). However, this method only shows the value in the "Computed" tab of the browser dev tools.
• Use a separate, unused numeric property to display the calculated value. This allows you to see the value directly in the "Styles" tab, but it's not a very convenient solution.

Additional Notes:

• The browser only calculates the final value of a calc() expression when it's used within a property. There's no single "computed value" that exists independently.
• JavaScript cannot provide the final calculated value because it varies depending on the property where it's used.

Here's a detailed explanation of formula validation and debugging techniques:

Formula Validation:

The CSS Calc() specification defines certain rules for combining different types in calculations:

• Addition/Subtraction: Both sides must have the same type (e.g., both lengths or both integers).
• Multiplication: At least one side must be a number.
• Division: The right side must be a number different from 0.

Any violation of these rules will result in an invalid expression.

Formula Debugging:

Unfortunately, there's no built-in debugging tool for CSS calc() formulas. However, you can adopt these strategies:

• Output Value to a Pseudo-Element: This allows you to check the computed value in the "Computed" tab of browser dev tools.
• Use an Unused Numeric Property: Assigning the calculated value to a separate property lets you inspect it directly in the "Styles" tab, but it's less convenient.

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