Functional Programming: Implement the filter Method on a Prototype returning a value

JavaScript
1

Tell us what’s happening:
I have the function prototype correctly filtering, but I am getting a filter of true or false upon each value, rather than the value itself. Is there a way to guide me along without giving answer away?

Your code so far


// The global variable
var s = [23, 65, 98, 5];

Array.prototype.myFilter = function(callback){
// Only change code below this line
var newArray = [];
for(let i=0; i < this.length; i++){
  newArray.push(callback(this[i]))
}
// Only change code above this line
return newArray;

};

var new_s = s.myFilter(function(item){
return item % 2 === 1;
});

console.log(new_s);

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/84.0.4147.125 Safari/537.36.

Challenge: Implement the filter Method on a Prototype

Link to the challenge:

2

FYI i can get the numbers to print, but only if i alter the bottom code and I don’t believe that’s correct as i’m only supposed to alter the code in between the commented out section

var s = [23, 65, 98, 5];

Array.prototype.myFilter = function(callback){
  // Only change code below this line
  var newArray = [];
  for(let i=0; i < this.length; i++){
    if(this[i] % 2 ===1){
    newArray.push(callback(this[i]))
  }
}
  // Only change code above this line
  return newArray;

};

var new_s = s.myFilter(function(item){
  return item 
}); 

console.log(new_s);
3

Hey, very nice exercise!
You get a boolean because of this return value:

return item % 2 === 1;

So, if I get your idea, this should return the item instead, maybe something like this:

return item % 2 === 1 && item;

pd: this will return false sometimes. So you probably should rewrite the conditional, using an if statement, and an empty else, or just the if statement.

4

the callback return boolean
if that boolean is true you want to keep the number, if it’s false you want to not keep the number
you do not want the boolean in the resulting array

@anon10002461: the challenge is to implement the filter method, your suggestion is off-topic and outside of allowed space to change

5

@ilenia I don’t know what you’re trying to say, but that’s fine…

6

this challenge has very specific instructions, your suggestion is totally off-topic and will make it even harder to pass the challenge

try yourself to pass the challenge following your suggestion: https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/functional-programming/implement-the-filter-method-on-a-prototype

7

I cant from my phone, and maybe i got it wrong, i’ve just read the post. Is it acceptable for you a mistake?

Normally, what I write has been helpful, so either reply me respectfully, or just don’t do it.

I guess maybe you’re learning english and that’s why it sounds bad. If that’s the case, don’t worry.

8

yes, a mistake is acceptable. But I hope you are not offended I point out a mistake to avoid even more confusion to the user asking for help

1 Like