fp-recursion

Functional programming requires recursion instead of loop. Writing recursion destracts sometimes developers from focusing more on business logic. So, to make use of recursion instead of loop and implement it easily the library can be used.

Install

npm install --save fp-recursion

Usage

import { recurEach, recurTill, recurWhile } from 'fp-recursion';

OR

const { recurEach, recurTill, recurWhile } = require('fp-recursion');

recurEach

Iterates for each element of source array and generates new value based on initial value.

• Systax

recurEach(
    srcArray, // oprFunc will be called for each element of the source array
    idx, // Default value is 0. Index from which evaluation starts.
    incr, // Default value is 1. Increment value to evaluate next element
    till // Used if it passed and oprFunc will be called for each element till the value or source array length whichever is less
).initVal( //The function accepts initial value
    value, // The value will be passed to oprFunc and the function should return new computed value which again will be passed to oprFunc on next iteration. The process continues untill recursion ends. The value can be any of type e.g. Array, Object, Primitive
).opr(
    oprFunc, // The function will be executed for each element of the source array, with initial value / computed value
);

• oprFunc

oprFunc(
    ele, // Element of source array
    value, // To be used to compute a new value and the new value should be returned from the function. The returned value will be passed here in next iteration
    idx, // Current index
    srcArray //Whole source array for handling some unexpected scenario
) // The function should return a new computed value

• Example

const srcArr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
const resArr = recurEach(srcArr)
    .initVal([])
    .opr((val, arr) => [...arr, val + 1]);
console.log(resArr); // [2, 3, 4, 5, 6, 7, 8, 9, 10, 11]

There are two ways to pass initial value.

1. You can pass it into initVal.
2. You can use default argument of oprFunc as shown below.

recurEach(srcArr)
    .opr((val, arr = []) => [...arr, val + 1]);

But, if source array is empty in that case second way will return undefined if you dont handle the case in oprFunc. So, first way is recommended to pass initial value.

recurTill

Iterates for no. of till value and generates new value based on initial value.

• Syntax

recurTill(
    till, // No. of times the oprFunc be called
    idx, // Default value is 0. Index from which evaluation starts.
    incr // Default value is 1. Increment value to evaluate next element
).initVal( //The function accepts initial value
    value, // The value will be passed to oprFunc and the function should return new computed value which again will be passed to next iteration of oprFunc. The process continues untill recursion ends. The value can be any of type e.g. Array, Object, Primitive
).opr(
    oprFunc, // The function will be executed for each index till `till` value
)

• oprFunc

oprFunc(
    idx, // Currennt index
    value, // To be used to compute a new value and the new value should be returned from the function. The returned value will be passed here in next iteration
    till // No. of times of recursion
) // The function should return a new computed value

• Example

const resArr = recurTill(10)
    .initVal([])
    .opr((idx, arr) => [...arr, idx * 2]);
console.log(resArr); //[0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

There are two ways to pass initial value.

1. You can pass it into initVal.
2. You can use default argument of oprFunc as shown below.

recurTill(10)
    .opr((val, arr = []) => [...arr, val + 1]);

But, if till value is 0 in that case second way will return undefined if you dont handle the case in oprFunc. So, first way is recommended to pass initial value.

recurWhile

Iterates till condition isn't be false and generates new value based on initial value.

• Syntax

recurWhile(
    conFunc, // The function has initial value as parameter and returns `true` or `false`. If it returns `true` recursion continues otherwise starts returning
).initVal( //The function accepts initial value
    value, // The value will be passed to oprFunc and conFunc. conFunc should return boolean and oprFunc should return new computed value which again will be passed to next iteration of oprFunc and conFunc. The process continues untill recursion ends. The value can be any of type e.g. Array, Object, Primitive
).opr(
    oprFunc, // The function will be executed untill conFunc returns `false`
)

• conFunc

conFunc(
    value //Based on the value the function should return either `true` or `false`
)

• oprFunc

oprFunc(
    value, // To be used to compute a new value and the new value should be returned from the function. The returned value will be passed here and in conFunc in next iteration
) // The function should return a new computed value

• Example

const res = recurWhile((val) => val !== 10)
        .initVal(0)
        .opr((val) => val + 1);

console.log(res); //10

We cannot pass initial value as default argument with recurWhile.

Please check test cases for more examples.