computed-style-to-inline-style | Convert a HTML element 's computed CSS to inline CSS

We have a corporate content management system that allows for rich text editing/html markup, but does not allow for head elements or style sheets to be uploaded, attached, or used in any way. It provides some rich text editing controls and also access to the source html, but just for the html fragment -- there is no head, no body. We also have no access the whole system that presents these bits of markup on the page. The only way to style the content is through inline style attributes on the elements. It is best, it isn't pretty, but that is what we have and I'm trying to make the best of a bad situation.

We also have high standards for visual presentation and would like to be able to quickly produce and modify/update content and keep it looking nice. It is difficult to correctly apply formatting using the system. For anybody who has tried to markup anything more than a paragraph or two with an RTE, you probably know what I mean. It seems like we should have a different system, but has anybody worked for a large company before? Just sayin.

We do have access to another location where we could "author" and "store" actual styled content and then "compile it" for copypasta into the other system. In other words, we could author/design using css and best practices and then we could run some code that could convert those element, class, and id formatting into inline styles.

I did my research and found this thread which also lead me to this code.

These both are very helpful in exploring solutions, but I've run into an issue. These solutions use the javascript getComputedStyle() method. There are some other options for properties to only look at other properties or to be recursive on the children of the element provide, but basically it boils down to this. (Since getComputeStyle returns an object and not an array, there is also a prototype/polyfill to allow iterating over an object with forEach, but none of that is part of the issue I'm facing.)

const computedStyle = getComputedStyle(element); computedStyle.forEach(property => { element.style[property] = computedStyle.getPropertyValue(property); });

This works well for css attributes like font-size:24px or margin:0 15px. The issue I'm running into are when I'm using units other than px. For example, if I'm trying to make something that has width:50%. getComputedStyle() converts the 50% to the actual number of pixels that 50% is currently using.

In the notes section of the MDN web docs I see that this is expected behavior. Although I'm not quite clear on what that last line means.

...An example difference between pre- and post-layout values includes the resolution of percentages for width or height, as those will be replaced by their pixel equivalent only for used values.

So what I'm trying to do is convert something like this

.container{width:50%;}

into something like this

Does anyone know of a way to complete this type of transformation?

PS: If it matters we'll be using the more basic attributes in our css -- no transitions, grid, prefixing, etc. We still need to support IE 11 -- if that tells you anything. We won't need to account for every edge case or browser. Just some basic stuff so that all our H1 look the same.