The new Spartan browser in Windows 10 is a major departure for Microsoft. As Simon Bisson noted in his first look of Spartan last week, the browser features both a new JavaScript engine and a new rendering pipeline, along with a sleek, fresh look. Bisson also noted, however, that Spartan fared only slightly better in HTML5 compatibility tests than IE 11 -- behind Chome, Opera, Firefox, and Safari, in that order.

But that's by no means the end of the story. To get a deeper assessment of Spartan's innards, I turned to Steve Newcomb and Mike O'Brien of Famo.us, whose wildly innovative JavaScript framework won an InfoWorld Technology of the Year Award. Newcomb, Famo.us's CEO, told me that "the whole team is super excited about Spartan" and that he's already considering making Spartan the browser of choice for demos.

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That's quite a turnaround after Famo.us's long frustration with IE. O'Brien, head of platform for Famo.us, says the new Chakra JavaScript engine in Spartan "seems to just be hands down the fastest JavaScript engine out there now."

Asked for a more specific speed assessment on a scale from 0 to 10, O'Brien says, “Let’s say Firefox is a 5, Chrome is a 6 ... Safari and Spartan would both probably be around 8 ½."

O'Brien also praises Spartan's rendering performance: "You know if they understand rendering well by things like anti-aliasing. So if I have a diagonal line on the screen, how pixelated does that thing look? On Spartan it looks really, really nice; on Firefox it looks really, really terrible ... [Spartan] passed all our tests and drew everything the way that we thought it should be drawn."

All this is somewhat puzzling, because ostensibly, the JavaScript and rendering engines in Spartan had already been introduced in IE 11. O'Brien speculates that "it seems like they’ve torn the majority of it out, and kind of what’s left is the scaffolding they would have had to rewrite anyway ... After talking with their engineers, they have some really advanced stuff going on, [including] hardware rendering for the pipeline."

Other improvements, say Newcomb and O'Brien, include better developer tools. O'Brien thinks Microsoft has a way to go before catching Google Chrome's developer tools, which he considers best among browsers, but Spartan is already ahead of Safari. He's also impressed by the way Microsoft is driving CSS3 standardization.

Newcomb can't resist amplifying this last point: "Microsoft always used to be non-compliant to anything ... Microsoft for the first time is actually driving towards standards and ubiquity instead of going its own way."

Dealing with Microsoft is not a new experience for Newcomb. Seven years ago, he was instrumental in selling the semantic search startup he co-founded, Powerset, to Microsoft for a rumored $100 million. When asked to contrast his past dealings with the openness he's seen from Microsoft lately, Newcomb says, "It doesn't feel like Microsoft at all."