Why Javascript is used in MongoDB or CouchDB instead of other languages such as Java, C++?

Question

My understanding of the Javascript so far has been that it is a client-side language that capture events and makes a web-page dynamic.

But on reading the comparison between MongoDB, and CouchDB (http://www.mongodb.org/display/DOCS/Comparing+Mongo+DB+and+Couch+DB ) I noticed that both are using JS. This makes me wonder the reason behind the choice of JS over other conventional languages.

I guess I am trying to understand the role of JS and its advantages over other languages.

Update: I am not asking about the languages/drivers supported by the two dbs. The comparison says--"Both CouchDB and MongoDB make use of Javascript. CouchDB uses Javascript extensively including in the building of views ....MongoDB also supports running arbitrary javascript functions server-side and uses javascript for map/reduce operations."

My lack of understanding pertains to why is JS being used at all for the backend work. Why is it preferred for building views in CouchDB, or for using map/reduce operations? Why C/C++ or Java were not used? What are the advantages in using JS for such back-end work?

Answer:To summarize answers on https://softwareengineering.stackexchange.com/q/121411/41398 . MongoDB and other NoSQL dbs are using SpiderMonkey to execute server-side JS functions. Here is the wikipedia's link to spidermonkey- http://en.wikipedia.org/wiki/SpiderMonkey_(JavaScript_engine)

PS: If somebody feels like down-voting the question, please do put a comment to explain the reason.

Answer 1

The issue with many languages is a lack of sandboxing (being able to do 'rm -rf /' in a map function is considered a problem), javascript, because of its browser roots, has one. Javascript is the default view server in CouchDB but the protocol is documented and other language bindings exist (Ruby, Python, etc). It also ships with a native Erlang option.

There's also an elegance to using the same language at the back-end as the front-end but CouchDB doesn't force you into a language choice, it just ships with a solid Javascript view engine.

Details on the view server protocol, and links to alternate implementations, here:

http://wiki.apache.org/couchdb/View_server

Answer 2

Because it's the language they chose?

• It's (reasonably) dynamic.
• Functions can be passed around.
• Open, embeddable implementations exist.
• It's ubiquitous.
• Using JSONy data model.

There aren't a lot of great options for "live" evaluation (IMO): Lua, Scheme-y things, and JS are probably the best choices for C programs.

If it had been written in Java, there is a default scripting layer "built in".