Bug 239579

Try this code: var s = document.body.style; var cs = getComputedStyle(document.body); s.cssText = "mask-clip: content-box"; cs.maskClip; // "content-box" s.cssText = "-webkit-mask-clip: initial; mask-clip: content-box"; cs.maskClip; // "border-box" s.cssText = "mask-composite: exclude"; cs.maskComposite; // "exclude" s.cssText = "-webkit-mask-composite: initial; mask-composite: exclude"; cs.maskComposite; // "add" s.cssText = "mask-mode: alpha"; cs.maskMode; // "alpha" s.cssText = "-webkit-mask: initial; mask-mode: alpha"; cs.maskMode; // "match-source" s.cssText = "overflow-wrap: anywhere"; cs.overflowWrap; // "anywhere" s.cssText = "word-wrap: initial; overflow-wrap: anywhere"; cs.overflowWrap; // "normal" s.cssText = "text-combine-upright: all"; cs.textCombineUpright; // "all" s.cssText = "-webkit-text-combine: initial; text-combine-upright: all"; cs.textCombineUpright; // "none" This should not happen, the legacy properties should be implemented as one of - Aliases - Shorthands - Deferred properties See https://drafts.csswg.org/css-cascade-4/#aliasing Then the last used property would take precedence, as such: s.cssText = "word-wrap: break-word; overflow-wrap: anywhere"; cs.wordWrap; // "anywhere" (not "break-word"!!!) cs.overflowWrap; // "anywhere" (not "break-word"!!!) s.cssText = "overflow-wrap: anywhere; word-wrap: break-word"; cs.wordWrap; // "break-word" cs.overflowWrap; // "break-word"