It's a utility library for JS. Consider that the article mentions Python's itertools and functools as equivalents. http://underscorejs.org/ http://underscorejs.

It's a utility library for JS. Consider that the article mentions Python's itertools and functools as equivalents. http://underscorejs.org/ http://underscorejs.org/ does a good job: """ Underscore is a JavaScript library that provides a whole mess of useful functional programming helpers without extending any built-in objects. It’s the answer to the question: “If I sit down in front of a blank HTML page, and want to start being productive immediately, what do I need?” … and the tie to go along with jQuery's tux and Backbone's suspenders. Underscore provides 80-odd functions that support both the usual functional suspects: map, select, invoke — as well as more specialized helpers: function binding, javascript templating, deep equality testing, and so on. It delegates to built-in functions, if present, so modern browsers will use the native implementations of forEach, map, reduce, filter, every, some and indexOf. """