Title casing a sentence

Question

Code:

function titleCase(str) {
let a = str.concat();
a = a.toLowerCase().split(" ");

let v = a.map(function(item){
item[0] = item[0].toUpperCase();
return item;
});
 
return v.join(" ");
}

console.log(titleCase("I'm a little tea pot"));//output should be "I'm A Little Tea Pot" but shows "i'm a little tea pot"

The code should simply show the output as indicated in the comment on the last line. The value of item[0] is not changing.

This was actually one of a challenge to complete on a website which required not to change the original string. — Prakhar Saxena, Jun 14 '18 at 18:54
Altering a string is not going to change the original that you pass in. Learn about pass by reference/ pass by value. — epascarello, Jun 14 '18 at 18:55
Possible duplicate of [Convert string to title case with JavaScript](https://stackoverflow.com/questions/196972/convert-string-to-title-case-with-javascript) — kano, Jun 15 '18 at 04:18

baao · Accepted Answer · 2018-06-14T18:57:39.730

2

You can do this pretty easy and fast with a little regex

function titleCase(str) {
  return str.replace(/\s(\w)|^(\w)/g, e => e.toUpperCase())
}

console.log(titleCase("i'm a little tea pot"));

Your code doesn't work because a string is immutable, meaning you can't assign a new value to it like that. If you want to keep your loop, you can use below instead

function titleCase(str) {
  return str.split(' ').map(function(item){
    item = item.substring(0,1).toUpperCase() + item.substring(1);
    return item;
  }).join(' ');
}

console.log(titleCase("I'm a little tea pot"));

edited Jun 14 '18 at 18:57

answered Jun 14 '18 at 18:53

baao

71,625
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At first, I did use regex to change the case of the sentence which worked. Then, I tried to change the case using the `map()` function to alter the content of the string which didn't actually work. Your code worked and I actually used `return item[0].toUpperCase() + item.slice(1)`. – Prakhar Saxena Jun 14 '18 at 19:16

score 1 · Answer 2 · answered Jun 14 '18 at 19:00

1

You can also correct your method like following

function titleCase(str) {
  return str.toLowerCase().split(" ").map(s => s[0].toUpperCase() + s.slice(1)).join(" ");
}

console.log(titleCase("I'm a little tea pot"));

answered Jun 14 '18 at 19:00

Nikhil Aggarwal

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score 0 · Answer 3 · answered Jun 14 '18 at 18:57

item is a string. Strings are immutable. In particular, you cannot assign to individual characters to change the string. That's why item[0] = ... has no effect.

There are a couple of ways you could do this instead.

Build a new string instead of trying to modify item in place:

function titleCase(str) {
  const a = str.toLowerCase().split(" ");

  const v = a.map(function(item) {
    return item[0].toUpperCase() + item.substr(1);
  });

  return v.join(" ");
}

console.log(titleCase("I'm a little tea pot"));

Or just use a regex search/replace:

function titleCase(str) {
  return str.replace(/(^|\s)(\w)/g, function(m0, m1, m2) {
    return m1 + m2.toUpperCase();
  });
}

console.log(titleCase("I'm a little tea pot"));

score 0 · Answer 4 · answered Jun 14 '18 at 18:59

Add a few console.log() to debug your code along the way. It'll help you see how your string transforms.

   function titleCase(str) {
      // let a = str.concat(); // No need to concat a string.
      let words = str.toLowerCase().split(" ");

      // item is individual words
      let v = words.map(function(item){
        let title = item.charAt(0).toUpperCase() + item.slice(1) // You need to select letters by charAt(...)
        return title;
      });

      return v.join(" ");
    }

    console.log(titleCase("I'm a little tea pot"));

Title casing a sentence

4 Answers4