JS toLowerCase() not working

Question

I have this code :

//make first letter of each word capital
function titleCase(str) {
    /*
     *  1. change all letters to lower case
     *  2. split words
     *  3. set each 1st letter to Capital
     *  4. combine array back into string
     */
    arr = [];
    str.toLowerCase();

    arr = str.split(" ");

    for (var index = 0; index < arr.length; index++) {
        arr[index].charAt(0).toUpperCase();
    }

    str= arr.join(" ");
    return str;
}
console.log(titleCase("Potato potato potato"));

And I don't understand why toLowerCase() and toUpperCase() are not working. What am I doing wrong ?

`toLowerCase()` and `toUpperCase()` does not affect the value of the string `str` itself. You need to assign back the value to `str` after converting to lower case or upper case. — Hassan Imam, Sep 26 '17 at 13:56
Possible duplicate of [Title case a sentence?](https://stackoverflow.com/questions/31495239/title-case-a-sentence) — Rajesh, Sep 26 '17 at 13:56

Nikhil Aggarwal · Accepted Answer · 2017-09-26T14:12:03.797

3

There are 2 updates required

Reassign str.toLowerCase() to str
Reassign updated array value back in array.

Please note, until and unless you reassign the values, the original value does not change. Hence, the result remained unaffected.

//make first letter of each word capital
function titleCase(str) {
/*
1. change all letters to lower case
2. split words
3. set each 1st letter to Capital
4. combine array back into string
*/
    arr = [];
    str = str.toLowerCase(); // **** Problem 1 - Reassigning

    arr = str.split(" ");

    for (var index = 0; index < arr.length; index++) {
       // **** Problem 2 - Reassigning
       arr[index] = arr[index].charAt(0).toUpperCase() + arr[index].slice(1);
    }

    str= arr.join(" ");
    return str;
}
console.log(titleCase("Potato potato potato"));

edited Sep 26 '17 at 14:12

answered Sep 26 '17 at 13:55

Nikhil Aggarwal

28,197
4
43
59

the solution is so much overcomplecated. – Joshua K Sep 26 '17 at 14:09
1

@Durga - Agreed & Updated. Thanks! – Nikhil Aggarwal Sep 26 '17 at 14:12
@JoshuaK - Correct, however, this brings the solution with minimal change in original code. – Nikhil Aggarwal Sep 26 '17 at 14:14

Jeremy Thille · Answer 2 · 2017-09-26T14:02:18.120

You need to reassign (overwrite) the value inside the array after you change it. Otherwise, the array remains unchanged. Besides, you forgot to add the rest of the string (arr[index].slice(1)) to the uppercased letter.

function titleCase(str) {
    let arr = [];
    str.toLowerCase();

    arr = str.split(" ");

    for (var index = 0; index < arr.length; index++) {
        arr[index] = arr[index].charAt(0).toUpperCase() + arr[index].slice(1); // <-- Changes
    }

    str= arr.join(" ");
    return str;
}
console.log(titleCase("Potato potato potato"));

EDIT

Here is my own ES6 one-liner version :

titleCase = str => str.trim().split(" ").map( word => word.charAt(0).toUpperCase() + word.slice(1) ).join(" ")
    
console.log(titleCase("Potato potato potato"));

Explanation :

titleCase = str => str
                   .trim() // Removes extra spaces
                   .split(" ")
                   .map( word =>
                        word.charAt(0).toUpperCase() + word.slice(1) // Uppercases 1st letter, adds the rest of the word, returns the whole
                   )
                   .join(" ") // Reforms a string

Just a pointer. Do not rush into posting an answer. An answer is incomplete without explanation. This attracts unwanted votes/comments like this. Its a good practice to incrementally update answer, but make sure your 1st cut justifies the term answer — Rajesh, Sep 26 '17 at 13:59
you forgot to lowercase the rest of the words in your one liner solution. Again: Don't rush. Think about your solution and post it when you are ready. — Joshua K, Sep 26 '17 at 14:10

Joshua K · Answer 3 · 2017-09-26T14:03:10.807

0

short solution:

var titleCase = (str)=>str.toLowerCase().split(' ').map(word=>word.charAt(0).toUpperCase()+word.slice(1)).join(' ');

calling:

titleCase('Potato potato potato');

Splitting the string by space and map a lambda to the resulting array. The lambda turns up the first letter and append the rest of the word.

as pointed out in the comments:

var titleCase = (str)=>str.toLowerCase().split(' ').reduce((currentString, word)=>currentString+(currentString ? ' ':'')+word.charAt(0).toUpperCase()+word.slice(1));

this works also and loops only one time.

edited Sep 26 '17 at 14:03

answered Sep 26 '17 at 13:59

Joshua K

2,407
1
10
13

Reduce would suit more. `.map` + `.join` means you are looping twice – Rajesh Sep 26 '17 at 14:00

score 0 · Answer 4 · answered Sep 26 '17 at 14:03

0

you can simply do

function convert(str){
    return str.split(' ').map(e => e.replace(/([A-Za-z])(\w+)/, (x, y, z) => y.toUpperCase()+z.toLowerCase())).join(' ');
}

console.log(convert('Potato potato pOtato'))

answered Sep 26 '17 at 14:03

marvel308

10,288
1
21
32

JS toLowerCase() not working

4 Answers4