concat-each

Iterates nested loops and concatenates values onto an Array or Set.

Installation

Requires Node.js 8.3.0 or above.

npm i concat-each

API

The module exports a single function.

Parameters

1. base (Array, Set, WeakSet): The collection onto which new items should be concatenated. If you want to create a new collection, pass in [] or new Set() or new WeakSet().
2. Variadic: ...iterables (one or more of: iterable): Iterable collections of items to pass to cb. Specify multiple iterables if you want nested loops.
3. cb (function): A callback which accepts an argument for each iterable in iterables and returns an array of items to concatenate onto base.
4. Optional: Object argument:
   • arrays / sets / weakSets (arrays of classes/strings): Arrays of classes and/or string names of classes that should be treated as equivalent to Array/Set/WeakSet (respectively).
   • loose (boolean): Whether or not to compare values loosely (as defined by looselyEquals) for the purpose of testing uniqueness if unique is true. Defaults to false.
   • looselyEquals (function): A callback that accepts two values and returns true if they are to be considered equivalent or false otherwise. This argument is only used if loose is true. If omitted, the default behavior will, among other things, consider arrays/objects to be equal if they have the same entries.
   • unique (boolean): Whether or not to refrain from adding values that already exist in base. Defaults to false. You can define what uniqueness means by using the loose and looselyEquals arguments.

Return Value

Modifies and returns base.

Example

Explaining the module is best done by showing the code it replaces:

Before

const n = []
for (const i of [1, 2, 3]) {
  for (const j of [2, 3, 4]) {
    const sum = i + j
    if (sum % 2 === 0) n.push(sum)
  }
}

n // [4, 4, 6, 6]

After

const concatEach = require('concat-each')

const n = concatEach([], [1, 2, 3], [2, 3, 4], (i, j) => (i + j) % 2 === 0 ? [i + j] : []) // [4, 4, 6, 6]

Related

• neach: Nested forEach