2.0.0 • Public • Published


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map, reduce, forEach, and filter for plain objects. Lazy evaluation, supports functional and imperative syntax, no dependencies.

Why should you care?

I wanted a library that has no dependencies and gives me the basic map/reduce/filter for use on objects. Any existing library I found has boatloads of dependencies, provides tons more extra tools, and/or is unmaintained. So here's ObjectFn, just for you!

Also, big props to @declandewet for the initial implementation of this library!



Using a terminal:

$ npm install objectfn -S


Usage is straightforward. Just import what you need and use it on an object.

Imperative style

Takes data first, callback last.

const {map, reduce, filter, forEach} = require('objectfn')
const obj = { foo: 'bar', wow: 'doge' }
map(obj, (val) => val.toUpperCase())
// { foo: 'BAR', wow: 'DOGE' }
reduce(obj, (acc, val, key) => (acc[key.toUpperCase()] = val, acc), {})
// { FOO: 'bar', WOW: 'doge' }
filter(obj, (val, key) => key !== 'foo')
// { wow: 'doge' }
forEach(obj, console.log.bind(console))
// bar foo 0 { foo: 'bar', wow: 'doge' }
// doge wow 1 { foo: 'bar', wow: 'doge' }

Functional style

Takes callback first, data last. Each method is automatically curried.

const {map, reduce, filter, forEach} = require('objectfn')
const obj = { foo: 'bar', wow: 'doge' }
const upcaseValues = map((val) => val.toUpperCase())
// { foo: 'BAR', wow: 'DOGE' }
const upcaseKeys = reduce((acc, val, key) => (acc[key.toUpperCase()] = key, acc), {})
// { FOO: 'bar', WOW: 'doge' }
const ignoreFoo = filter((val, key) => key !== 'foo')
// { wow: 'doge' }
const logValues = forEach(console.log.bind(console))
// bar foo 0 { foo: 'bar', wow: 'doge' }
// doge wow 1 { foo: 'bar', wow: 'doge' }

Method Signature

  • Each callback has a method signature of (value, key, index, object) with the exception of reduce.
    • value is the current key's value
    • key is the current key's name
    • index is the 0-based index of the current key
    • object is the original object.
  • reduce has a method signature of (accumulator, value, key, index, object).
    • accumulator is any initial value onto which you want to iteratively reduce from object.

Differences in reduce

In objectfn, the act of passing an accumulator to the reduce method is required, which is better for readability/accessibility (developer intentions are made more obvious), has no immediate disadvantages and is one of the two reasons objectfn is able to support both functional and imperative syntaxes.

This means that this will work:

let obj = { one: 1, two: 2, three: 3, four: 4 }
reduce(obj, (acc, val) => acc + val, 0) // => 10

But this will not:

let obj = { one: 1, two: 2, three: 3, four: 4 }
reduce(obj, (prevVal, currVal) => prevVal + currVal) // => wat?

Binding this

objectfn offers no mechanism for binding the this context of the callback via the last parameter. This is one of two reasons why objectfn is able to support both functional and imperative syntaxes. If you want this behavior, it is still possible (and far more readable) to do so using Function.prototype.bind:

map(obj, fn.bind(/* value to use as `this` goes here */))

License & Contributing


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  • jescalan
  • declandewet