Split join, why will this not work?

Tell us what’s happening:
At the risk of sounding dumb, could someone explain where my code goes wrong?

Your code so far

function sentensify(str) {
// Add your code below this line
return str;
// Add your code above this line

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.87 Safari/537.36.

Challenge: Combine an Array into a String Using the join Method

Link to the challenge:

Remember that the split and join methods return values. They do not mutate the original value in which they are called. Also, you should research the join method a bit more to understand what arguments you can/should pass to it in order to solve this challenge.

Is that to suggest that what I am currently doing is only effective if I’m working on mutable items?

Also, I noticed it’s possible to chain multiple methods like split, join, reduce, etc on the same variable but have a line separating each method for ease of readability? I tried doing something similar and couldn’t get it to work.


return title
  .split ()

As @RandellDawson suggested, split and join return a new value, and DO NOT mutate the original input:
this means:

var s = 'Batman, Batman';

const splitted = s.split(', ') // works
console.log(s) // 'Batman, Batman'
console.log(splitted) // [ 'Batman', 'Batman' ]

So the original s is still unchanged, meaning the the next line of code:

s.join() // TypeError: s.join is not a function

will fail since string don’t have a join method.

When you chain multiple methods, you are calling the next function on the previous returned value, with the caveats that the first method must be on the same line, otherwise the JS interpreter won’t understand if you are declaring a new variable or doing something:

var someHtmlElement // you are declatrig a new undefined variable

However this is a practice that I personally discourage, I find it error-prone, bug prone and hard to debug.
And I can hardly see the advantage over the more verbose version :slight_smile:

const withColor = changeColor(prevHtml)
const withSize = changeSize(withColor) // <-- pass the return of the previous call
const someHtmlElement = changeContent(withSize) // both with color and size

Do you mean method chaining itself is something that is error-prone? Or is it the act of trying to method chain on separate lines?

last thing is, join also need an argument, or you will find yourself with a string made of a comma separated list

I meant the habit of chaining methods, I personally don’t like it that much, and I have found in my experience that it often causes me more errors that benefit.

But this is a totally biased opinion made by my own experience :slight_smile:

I find chained methods easier to read. But I usually write code with all the intermediate variables and then after everything works I chain things - much easier to debug


@Jengas2015, for me also it seems little bit confusion. What i did is to declare the variables before join.

function sentensify(str) {
  // Add your code below this line
  var myarray = str.split(/\W/); //this splits it by - this and my array is now `["May", "the", "force", "be", "with", "you"]
  var result = myarray.join(" ");` and this joins the array by spaces and make string again. and the value of variable result is now "May the force be with you"
  return result;
1 Like

How do you chain methods and do the thing where you have a line separating each method?




This is super helpful. Thank you very much for this.


like this
just remember that in a real situation there arguments that need to be added to those methods