Create chain in lodash with custom functions

Question

Is there way to get my own custom function in a chain of lodash. So for example like this:

var l = [1,2,3]
var add = function(a, b){return a+b}

var r =_.chain(l).find(function(a){return a>1}).add(5).value()

=>r = 7

Answer 1

What you look for is a way to extend the lodash prototype. It so nicely turns out that you can do it easily with a mixin utility function. Check here the docs: http://lodash.com/docs#mixin

In your example it will look like:

var l = [1,2,3];
var  add = function(a, b){return a+b}


_.mixin({
    add: add 
});


var r =_.chain(l).find(function(a){return a>1}).add(5).value()
console.log(r); ==> 7

and here is live sample on fiddle: http://jsfiddle.net/g2A9C/

Answer 2

After @stride anwswer I came up with a more generic solution using _.mixin:

function add(a, b, c) {
  return a + b + c
}

function sub(a, b, c) {
  return a - b - c
}

_.mixin({
  run: function (v, f) {
    var args = Array.prototype.slice.call(arguments, 2)
    args.unshift(v)
    return f.apply(this, args)
  }
})
var r = _.chain(1).run(add, 1, 1).run(sub, 2, 2).value()

console.log(r) ->  -1
1 + 1 + 1 - 2 - 2 = -1

http://jsbin.com/iyEhaMa/1/

After all I wonder why this not a build in function in lodash.

Answer 3

Another option is to just drop chaining and leverage function composition through _.flow.

From the DOCS:

[Flow] Creates a function that returns the result of invoking the given functions with the this binding of the created function, where each successive invocation is supplied the return value of the previous.

This means that every function inside Flow will receive as input the output of the previous one. In practice this means we are not limited to using only Lodash API methods, but we can mix and match whatever function we fancy, as long as the next one is able to handle that return value.

var l = [1,2,3]
var add = _.curry((a, b) => a + b);

_.flow(
  _.find(a => a > 1),
  add(5),
)(l);

// => 7

NB - This example is using the Functional version of Lodash, if you don't want or can't use that one you can still achieve the same result, check my other answer to another question about Lodash.