FreeCodeCamp/HelpJavaScript

Get help on our basic JavaScript and Algorithms Challenges. If you are posting code that is large use Gist - https://gist.github.com/ paste the link here.

Dan Couper

@DanCouper

[1,2,3].filter(value => value > 1) - this returns [2,3] because those are the values greater than one - the function given says return true if the value is greater than 1

And re Boolean

mitchell369

@mitchell369

but merely passing Boolean through the function is sufficient to produce this interpretation... no comparison operators necessary...

Dan Couper

@DanCouper

Boolean(0) returns false, Boolean(1) returns true, Boolean(null) returns false, Boolean("hello") returns true

https://developer.mozilla.org/en-US/docs/Glossary/Truthy

The Boolean function coerces anything you give it to true or false according to the rules of JS

mitchell369

@mitchell369

Yah I tihnk I get it, it already has a defined set of rules to produce true and false, filter only produces values that are assigned as true

true is already pre-defined in the function

thank you @DanCouper

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@camperbot

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Dan Couper

@DanCouper

There is another aspect to this - the Boolean function is used by JS under the hood for filter anyway - anything you give to filter, JS will try to convert to true or false to make sure that it doesn't blow up, that it always returns something. So you can do

`arr.fipt

arr.filter(value => value)

i.e. a function that just returns the value you give it

Because

Filter already takes that value and converts it to true or false

mitchell369

@mitchell369

are you saying arr.fipt == arr.filter (value => value) ?

Markus Kiili

@Masd925

@mitchell369 arr.filter (value => value) filters in truthy array elements, the same as arr.filter (Boolean).

Dan Couper

@DanCouper

arr.fipt is me mistyping @mitchell369

mitchell369

@mitchell369

Good afternoon goyim. Can any of you good goys help me work of why my if statement is n't evaluating non-alpha characters in my code?

function rot13(str) { // LBH QVQ VG!
var numStr = str.split("").map(function (char) {

return String.fromCharCode(64 < char < 72 ? char.charCodeAt() % 26 + 65 : char);
});
return numStr;
}

I have passed through values like ' and it wants to assign them the samevalue as "A"

Stephen James

@sjames1958gm

@mitchell369 64 < char < 72 this is not valid syntax

@mitchell369 Well it is not testing what you want.
What you end up with is essentially (64 < char) < 72 which is testing true/false < 72

mitchell369

@mitchell369

@sjames1958gm ok, I can understand that as someone who wasn't completely hopelessin math

Unwana Essien

@afixoftrix

hello there, I have a web pack/ babel problem
my loaders:

module: {
        loaders: [
            {
                test: /\.js$/,
                loader: 'babel-loader',
                query: {
                    presets: ['es2015']
                }
            }
        ]
    },

Here is the error I am getting:

^CMacBook-Pro:redux-learn Owner$ npm run-script watch

> redux-learn@1.0.0 watch /Users/Owner/Dev/Test Dump/redux-learn
> webpack --watch


Webpack is watching the files…

(node:2086) DeprecationWarning: loaderUtils.parseQuery() received a non-string value which can be problematic, see https://github.com/webpack/loader-utils/issues/56
parseQuery() will be replaced with getOptions() in the next major version of loader-utils.
Hash: e1004b9f03431443d6e6
Version: webpack 3.10.0
Time: 1232ms
             Asset     Size  Chunks             Chunk Names
    main.bundle.js   3.4 kB       0  [emitted]  main
main.bundle.js.map  2.46 kB       0  [emitted]  main
   [0] ./main.js 890 bytes {0} [built] [failed] [1 error]

ERROR in ./main.js
Module build failed: SyntaxError: Unexpected token (20:21)

  18 |     switch (action.type) {
  19 |         case "CHANGE_NAME": {
> 20 |             state = {...state, name: action.payload};
     |                      ^
  21 |             break;
  22 |         }
  23 |         case "CHANGE_AGE": {

Stephen James

@sjames1958gm

@mitchell369 You need 64 < char && char < 72 to have two numeric comparisons

mitchell369

@mitchell369

@sjames1958gm so can I use a colon after the first evalution then see if it is <|> ?

ok, I don't havemuch experience with && but I will give that a go

Stephen James

@sjames1958gm

@mitchell369 Just read && as AND

Unwana Essien

@afixoftrix

I don't understand why it doesn’t understand spread operator.

mitchell369

@mitchell369

@sjames1958gm That completely destroy the output lol

Stephen James

@sjames1958gm

@mitchell369 char.charCodeAt() % 26 + 65 what is this trying to do?

@afixoftrix I don't think spread operator is es2015
http://stefan.magnuson.co/articles/frontend/using-es7-spread-operator-with-webpack/

Markus Kiili

@Masd925

@sjames1958gm Spread operator is ES6 (ES2015).

mitchell369

@mitchell369

@sjames1958gm Its evaluating the remainder when I pass it through 26 character alphabet, I found that is the most effective method to produce the A => N conversion and Z => M or w/e it is. Adding the 65 get's you back to the Ascii recognized coding for A-Z

Unwana Essien

@afixoftrix

@mitchell369 Ok I just added babel ‘stage-3’ presets and it worked.

Stephen James

@sjames1958gm

@Masd925 Odd, it appears that for some reason babel doesn't work for objects like above with just es2015 preset

Markus Kiili

@Masd925

@sjames1958gm Compatibility of spread also differs depending on where/how it is used.

Stephen James

@sjames1958gm

@mitchell369 Why is the second number 72? and not 91 (one more than Z

mitchell369

@mitchell369

@sjames1958gm right on, good start... should be 92

Stephen James

@sjames1958gm

@mitchell369 BTW, your 64 < char && char < 72 is comparing the string value char not the char code of char

mitchell369

@mitchell369

@sjames1958gm That's a good lead, basically what I see it doing is changing all values that fall below that range into 65 and providing me with the output

Stephen James

@sjames1958gm

@mitchell369 You need to make sure that the types in your variables match the types you are comparing

mitchell369

@mitchell369

@sjames1958gm specifying the the limits within the charCodeAt(), seems to return hex values...

Stephen James

@sjames1958gm

@mitchell369 Your algorithm is close. just that the comparison should be with charCode not char

var c = char.charCodeAt();
return String.fromCharCode(64 < c && c < 91 ? c % 26 + 65 : c);

Ahmad Abdolsaheb

@ahmadabdolsaheb

hey everyone, I am trying to use filter, however, i want it to some times not filter anything. this is currently what i have

cards.filter(card=> card.type == "awards")

i have a variety of cards and sometimes i want filter to include all of the cards. how can I do that?

Ken Haduch

@khaduch

@ahmadabdolsaheb - without knowing all that you're doing, how about not calling the .filter when you don't want to actually filter, or if you make a "control" variable like this:

let doAll = true;
cards = cards.filter(card=> card.type == "awards" || doAll );

So that you can set doAll to the value you want (based on some condition) and then it would always pass the test? That's at least one take at it... You have to catch the return from the .filter, so I just threw that in there...

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