Get the default value of a css property

The function below returns the default value of CSS property for given tagName:

const getDefaultProperty = function(tagName, property) {
// Create new element
const ele = document.createElement(tagName);

// Append to the body
document.body.appendChild(ele);

// Get the styles of new element
const styles = window.getComputedStyle(ele);

// Get the value of property
const value = styles.getPropertyValue(property);

// Remove the element
document.body.removeChild(ele);

// Return the value of property
return value;
};

Good to know

The getComputedStyle() method returns the live styles of given element. It means that it's updated automatically if the element styles are changed.

That's why we need to get the value of property before removing the element. The following code doesn't return the correct value:

...
const styles = window.getComputedStyle(ele);
document.body.removeChild(ele);

// Always return "" because the element is already
// removed from the document
return styles.getPropertyValue(property);

We can use it, for example, to get the default font size of div tag:

getDefaultProperty('div', 'font-size');

// Or
getDefaultProperty('div', 'fontSize');

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