Couldn't understand the solution

JavaScript
#1

Tell us what’s happening:

I did not understand how reduce and map are working. Can really anyone explain in as easy as possible. please

Your code so far

      function whatIsInAName(collection, source) {
  // "What's in a name? that which we call a rose
  // By any other name would smell as sweet.”
  // -- by William Shakespeare, Romeo and Juliet
  var srcKeys = Object.keys(source);

  // filter the collection
  return collection.filter(function(obj) {
    return srcKeys
      .map(function(key) {
        return obj.hasOwnProperty(key) && obj[key] === source[key];
      })
      .reduce(function(a, b) {
        return a && b;
      });
  });
}

// test here
whatIsInAName(
  [
    { first: "Romeo", last: "Montague" },
    { first: "Mercutio", last: null },
    { first: "Tybalt", last: "Capulet" }
  ],
  { last: "Capulet" }
);

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/79.0.3945.88 Safari/537.36.

Challenge: Wherefore art thou

Link to the challenge:
https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/intermediate-algorithm-scripting/wherefore-art-thou

1 Like
#2

this is one of the cases in which you shoud try to follow the values using pen and paper, it would help you a lot

map is doing something with each element in the srcKeys returning a boolean for each element depending on conditions
reduce takes the array of booleans and returns true if everything is true inside the array, otherwise it returns false

#3

Your code has been blurred out to avoid spoiling a full working solution for other campers who may not yet want to see a complete solution. In the future, if you post a full passing solution to a challenge and have questions about it, please surround it with [spoiler] and [/spoiler] tags on the line above and below your solution code.

Please don’t do it again.

Thank you.

#4

I tried pen and paper i can understand that for first object in collection arr, { first: "Romeo", last: "Montague" }. map will check whether srcKeys value and key mathes this or not. If Yes then return ture, in the above case it return false. Then it goes to reduce now i don’t understand what is a and b here and why do we need reduce ?

Now i understand sorry

#5

reduce is needed to pass from an array of boolean to a single value
a and b are the accumulator and the current value of the reduce callback function

1 Like
#6

Got it thanks, so much

#7