Multi-map. Sometimes we want to look up an array from a key. This type of collection is sometimes called a multi-map. One key has multiple values. Program: We create an empty object with the identifier "test." We then invoke the add() function to add things to the object. Add: This function sees if an array exists at the requested key. If no ... MDN has further documentation on map, filter, reduce, and forEach. Other libraries. Some utility libraries like lodash and underscore offer similar methods, but you almost certainly don't need them. All modern Javascript runtimes and browsers have these functions available natively on array objects. Mar 28, 2016 · It implements a map function to operate on each element Its map function returns a functor of the same size That’s one to toss around at your next JavaScript Meetup.

Javascript array map() method creates a new array with the results of calling a provided function on every element in this array. This method is a JavaScript extension to the ECMA-262 standard; as such it may not be present in other implementations of the standard. To make it work, you need to add ...