Practical currying in Javascript

readme.md

Source examples for currying used in the article

https://www.linkedin.com/pulse/practical-currying-javascript-charl-marais

sum.js

A sum functions taking to arguments and returning the sum.

sum-currying.js

A sum function taking one argument and returning function that takes an argument and return the sum of the first with second.

advanced-filter.js

A filter method that filters out objects in an array that do not match all key/values of an input match object.

CodePen.io: https://codepen.io/talsmonkey/pen/rNOjbVW

advanced-filter-currying.js

A filter method that filters out objects in an array that do not match all key/values of an input match object. The implementation makes used of currying on array functions.

CodePen.io: https://codepen.io/talsmonkey/pen/dyYNrWv

advanced-filter-currying.js

function advancedFilter(collection, match) {
  const keysOf = obj => Object.keys(obj)
  
  const toKeyValue = obj => key => ({key, value: obj[key]});
  
  const matchKeyValue = keyValue1 => keyValue2 => 
      keyValue1.key === keyValue2.key && 
      keyValue1.value === keyValue2.value;

  const matchOnAll = keyValues => keyValue => keyValues.some(matchKeyValue(keyValue))
  // end functions
  
  const matchKeyValues = keysOf(match).map(toKeyValue(match));

  return collection.reduce((acc, cur) => {
    const curKeyValues = keysOf(cur).map(toKeyValue(cur));
    return matchKeyValues.every(matchOnAll(curKeyValues)) 
          ? [...acc, cur] 
          : acc
  }, []);
}

advanced-filter-use.js

const writePerson = item => document.write(`Name: ${item.name}, LastName: ${item.lastName}<br/>`);

const source = [{name:"Bruce", lastName:"Banner"}, 
  {name:"Bruce", lastName:"Wayne"}, 
  {name: "Clark", lastName: "Kent"}];

document.write("<h2>Source</h2>");
source.forEach(writePerson);

document.write("<br/>");
document.write("<h2>Filter on 'Bruce'</h2>");
advancedFilter(source, {name: "Bruce"}).forEach(writePerson);

document.write("<br/>");
document.write("<h2>Filter on 'Kent'</h2>");
advancedFilter(source, {lastName: "Kent"}).forEach(writePerson);

advanced-filter.js

function advancedFilter(collection, match) {
  const keysOf = obj => Object.keys(obj)
  
  const toKeyValue = (obj, key) => ({key, value: obj[key]});
  
  const matchKeyValue = (keyValue1, keyValue2) => 
      keyValue1.key === keyValue2.key && 
      keyValue1.value === keyValue2.value;

  const matchOnAll = (keyValues, keyValue) => keyValues.some(item => matchKeyValue(keyValue, item))
  // end functions
  
  const matchKeyValues = keysOf(match).map(item => toKeyValue(match, item));

  return collection.reduce((acc, cur) => {
    const curKeyValues = keysOf(cur).map(item => toKeyValue(cur, item));
    return matchKeyValues.every(item => matchOnAll(curKeyValues, item)) 
          ? [...acc, cur] 
          : acc
  }, []);
}

sum-currying-verbose.js

function sum(a) {
  function sumAWith(b) {
    return a + b;
  }
  return sumAWith;
}
console.log(sum(3)(5)); //prints 8

sum-currying.js

function sum(a) {
  return b => a + b; 
}
console.log(sum(3)(5)); //prints 8

sum.js

function sum(a, b) {
  return a + b;
}
console.log(sum(3, 5)); // prints 8