Uncaught SyntaxError: Duplicate data property in object literal not allowed in strict mode

[pjako]

I'm currently getting this error when I add web-animation.js to my index.html
web-animations.js:4546 Uncaught SyntaxError: Duplicate data property in object literal not allowed in strict mode

[alancutter]

I'm not able to reproduce this, could you give a code example that shows the error?
Which browser + version are you using?

[pjako]

I use chronium v40
This is how I tested it:
https://gist.github.com/pjako/f9d93b08504bb9c69576