/Web APIs


The CSSMathSum interface of the CSS_Object_Model#css_typed_object_model represents the result obtained by calling add(), sub(), or toSum() on CSSNumericValue.

A CSSMathSum is the object type returned when the StylePropertyMapReadOnly.get() method is used on a CSS property whose value is created with a calc() function.

CSSStyleValue CSSNumericValue CSSMathValue CSSMathSum


CSSMathSum() Experimental

Creates a new CSSMathSum object.

Instance properties


Returns a CSSNumericArray object which contains one or more CSSNumericValue objects.

Static methods

The interface may also inherit methods from its parent interface, CSSMathValue.

Instance methods

The interface may also inherit methods from its parent interface, CSSMathValue.

Event handlers



We create an element with a width determined using a calc() function, then console.log() the operator and values, and dig into the values a bit.

<div>has width</div>

We assign a width

div {
  width: calc(30% - 20px);

We add the JavaScript

const styleMap = document.querySelector("div").computedStyleMap();

console.log(styleMap.get("width")); // CSSMathSum {values: CSSNumericArray, operator: "sum"}
console.log(styleMap.get("width").operator); // 'sum'
console.log(styleMap.get("width").values); // CSSNumericArray {0: CSSUnitValue, 1: CSSUnitValue, length: 2}
console.log(styleMap.get("width").values[0]); // CSSUnitValue {value: 30, unit: "percent"}
console.log(styleMap.get("width").values[0].value); // 30
console.log(styleMap.get("width").values[0].unit); // 'percent'
console.log(styleMap.get("width").values[1]); // CSSUnitValue {value: -20, unit: "px"}
console.log(styleMap.get("width").values[1].value); //  -20
console.log(styleMap.get("width").values[1].unit); // 'px'

The specification is still evolving. In the future we may write the last three lines as:

console.log(styleMap.get("width").values[1]); // CSSMathNegate {value: CSSUnitValue, operator: "negate"}
console.log(styleMap.get("width").values[1].value); // CSSUnitValue {value: 20, unit: "px"}
console.log(styleMap.get("width").values[1].value.unit); // 'px'


Browser compatibility

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CSSMathSum 66 79 No No 53 No 66 66 No 47 No 9.0
CSSMathSum 66 79 No No 53 16.4 66 66 No 47 16.4 9.0
values 66 79 No No 53 16.4 66 66 No 47 16.4 9.0

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