How to Debug CSS `calc()` Expressions and Their Computed Values?

How to Debug Calculated CSS calc() Values?

Identifying Formula Errors

• Comply with CSS syntax rules for calc() operators to avoid invalid expressions.
• Ensure that variables and values adhere to type restrictions (e.g., numbers, integers, percentages).
• Remember that white space is required around and - operators.

Inspecting Computed Values

While there's no direct method to retrieve the computed value of a calc() expression, you can inspect the computed style properties that utilize it:

const elem = document.querySelector(".box");
const prop = window.getComputedStyle(elem, null).getPropertyValue("--variable"); // Value of the CSS variable using calc()
const height = window.getComputedStyle(elem, null).getPropertyValue("height"); // Actual rendered height.
console.log(prop);
console.log(height);

Debugging Example

For your specific formula transform: scale(var(--image-scale)) translateY(calc((1px * var(--element-height) * (var(--image-scale) - 1)) / 2 * var(--scrolled-out-y))):

• Confirm that all variables have valid values (e.g., numbers or properly defined types).
• Verify that the calc() expression operates on compatible types, following the rules mentioned earlier.
• Check if there are any potential JavaScript errors that may affect variable values before they are used in CSS.

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