Running examples results in "Undefined"

[jackcmay]

When attempting to run any of the rust-by-example examples the only output generated is the string "Undefined". The example on the rust home page works and the rust playground works.

Tried on safari and firefox with macos Yosemite.

[Arnavion]

Playground responds with HTTP 500 {"error":"Unable to deserialize request: Can't parse body to the struct"} because it's missing a backtrace: false property in the POST body. Adding that to the params object used in fetch() makes it work.

The parameter was added recently in rust-lang/rust-playground#364

https://github.com/rust-lang-nursery/mdBook/blob/d87e77ed/src/theme/book.js#L112-L119 needs to be updated, or playground needs to mark that with #[serde(default)]

cc @shepmaster

[frewsxcv]

Relevant issues: rust-lang/mdBook#751 rust-lang/rust#52871

[Arnavion]

Playground made the parameter optional to unbreak existing docs, and mdBook has updated to use the proper endpoint for new docs, so this can be closed now.