Throughout the book, we have used Lodash (https://lodash.com/) to illustrate how to manipulate data with generic functions. But there is nothing unique about Lodash. The exact same approach could be implemented via other data manipulation libraries or custom code.
Moreover, we used Lodash FP (https://github.com/lodash/lodash/wiki/FP-Guide) to manipulate data without mutating it. By default, the order of the arguments in immutable functions is shuffled. The code in listing D.1 is needed when configuring Lodash in order to ensure the signature of the immutable functions is exactly the same as the mutable functions.
This short appendix lists the 28 Lodash functions used in the book to help you, in case you are looking at a code snippet in the book that uses a Lodash function that you want to understand. The functions are split in to three categories:
Functions on maps in table D.1
Functions on arrays in table D.2
Function on collections (both arrays and maps) in table D.3
Each table has three columns:
Function shows the function with its signature.
Description provides a brief description of the function.
Chapter is the chapter number where the function appears for the first time.
Table D.1 Lodash functions on maps
Function
Description
Chapter
at(map,[paths])
Creates an array of values corresponding to paths of map
10
get(map,path)
Gets the value at path of map
3
has(map,path)
Checks if map has a field at path
3
merge(mapA,mapB)
Creates a map resulting from the recursive merges between mapA and mapB
3
omit(map,[paths])
Creates a map composed of the fields of map not in paths
10
set(map,path,value)
Creates a map with the same fields as map with the addition of a field <path,value>
4
values(map)
Creates an array of values of map
3
Table D.2 Lodash functions on arrays
Function
Description
Chapter
concat(arrA,arrB)
Creates an new array that concatenates arrA and arrB
5
flatten(arr)
Flattens arr a single level deep
14
intersection(arrA,arrB)
Creates an array of unique values both in arrA and arrB
5
nth(arr,n)
Gets the element at index n in arr
10
sum(arr)
Computes the sum of the values in arr
14
union(arrA,arrB)
Creates an array of unique values from arrA and arrB
5
uniq(arr)
Creates an array of unique values from arr
14
Table D.3 Lodash functions on collections (both arrays and maps)
Function
Description
Chapter
every(coll,pred)
Checks if pred returns true for all elements of coll
14
filter(coll,pred)
Iterates over elements of coll, returning an array of all elements for which pred returns true
3
find(coll,pred)
Iterates over elements of coll, returning the first element for which pred returns true
15
forEach(coll,f)
Iterates over elements of coll and invokes f for each element
14
groupBy(coll,f)
Creates a map composed of keys generated from the results of running each element of coll through f. The corresponding value for each key is an array of elements responsible for generating the key.
10
isEmpty(coll)
Checks if coll is empty
5
keyBy(coll,f)
Creates a map composed of keys generated from the results of running each element of coll through f. The corresponding value for each key is the last element responsible for generating the key.
11
map(coll,f)
Creates an array of values by running each element in coll through f
3
reduce(coll,f,initVal)
Reduces coll to a value which is the accumulated result of running each element in coll through f, where each successive invocation is supplied the return value of the previous
5
size(coll)
Gets the size of coll
13
sortBy(coll,f)
Creates an array of elements, sorted in ascending order by the results of running each element in coll through f
14
isEqual(collA,collB)
Performs a deep comparison between collA and collB
