How do I filter out a string to contain only letters in vanilla Javascript?

Question

I was given this string:

var myMessage = "Learning is fun!"

This is how I attempted to create an array listing only the letters (without the spaces and "!").

var myMessage = "Learning is fun!";
var arr1 = myMessage.split("");

function onlyLetters(array){
    let arr2 = []
    for(let i = 0; i < array.length; i++){
        if(array[i] === "a" || "b" || "c" || "d" || "e" 
        || "f" || "g" || "h" || "i" || "j" || "k" || "l" 
        || "m" || "n" || "o" || "p" || "q" || "r" || "s" 
        || "t" || "u" || "v" || "w" || "x" || "y" || "z"){
          arr2.push(array[i])
        }
    }
    return arr2
}

console.log(onlyLetters(myMessage))

What am I doing wrong? Also, is there a shorthand for listing letters "a" through "z"?

You can't do `array[i] === "a" || "b" || .... ` because the right side of the `===` is evaluated as `"a" || "b" || .... `. What you mean to do is `array[i] === "a" || array[i] === "b" || ...` — ninesalt, Oct 06 '19 at 17:23

Dhananjai Pai · Answer 1 · 2019-10-06T17:38:23.873

7

A simple way may be to use Regex like so

let message = "Learning is fun!";
let onlyLettersArray = message.split('').filter(char => /[a-zA-Z]/.test(char));
console.log(onlyLettersArray)

.filter takes an array and runs a function on the elements, which returns true or false. The item is removed if it returns false. The regex checks if the character is within the range a-z or A-Z

Another way is to filter the char and then split it like so

let message = "Learning is fun!";
let onlyLettersArray = message.replace(/[^a-z]+/gi, '').split('');
console.log(onlyLettersArray)

Edit:

var myMessage = "Learning is fun!";
var arr1 = myMessage.split("");

function onlyLetters(array){
    let arr2 = []
    for(let i = 0; i < array.length; i++){
        if(/[a-z]/.test(array[i])){ // you can use regex instead of all characters
          arr2.push(array[i])
        }
    }
    return arr2
}

console.log(onlyLetters(myMessage))

Update: If instead of an array of characters, you have to replace special chars in a string, you can write

let message = "Learning is fun!";
let letterMessage = message.replace(/[^a-zA-Z]/gm,"")
console.log(letterMessage)

edited Oct 06 '19 at 17:38

answered Oct 06 '19 at 17:24

Dhananjai Pai

5,914
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2

I'd argue that since OP is a beginner, it is more helpful to them to help with their existing code rather than give them something new. – ninesalt Oct 06 '19 at 17:25
I have given the explanation as well. I believe it may be a good way for them to learn the features javascript can offer as well. But you do have a valid point and I will update the code to add what the OP has used – Dhananjai Pai Oct 06 '19 at 17:26
I think he wanted an array of characters based on the question. If it is a string, you could replace the special chars @AZ_ – Dhananjai Pai Oct 06 '19 at 17:30
He hasn't used a join() in the end – Dhananjai Pai Oct 06 '19 at 17:31
1

You can also do `message.replace(/[^a-z]+/gi, '').split('')` – ninesalt Oct 06 '19 at 17:34
yeah @ninesalt that makes more sense too – Dhananjai Pai Oct 06 '19 at 17:39

AZ_ · Answer 2 · 2019-10-06T17:36:44.327

2

You simply can use String.prototype.match to get the array of letters only.

let arr = "Learning is fun!  1233  ashdgahsgdh".match(/[A-Za-z]/g);
console.log(arr)

edited Oct 06 '19 at 17:36

answered Oct 06 '19 at 17:33

AZ_

3,094
1
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it is String.prototype.match. Not array – Dhananjai Pai Oct 06 '19 at 17:35
1

@DhananjaiPai oops! typo – AZ_ Oct 06 '19 at 17:36

score 0 · Answer 3 · answered Oct 06 '19 at 17:35

You could take a lower case string, split it and check each character if the value is greater or equal to 'a' and smaller or equal to 'z'.

Ath the end, after filtering, you could get a string back by joining the array with an empty string as glue.

function onlyLetters(string) {
    return string
        .toLowerCase()
        .split("")
        .filter(c => c >= 'a' && c <= 'z')
        .join('');
}

console.log(onlyLetters("Learning is fun!"));

score 0 · Answer 4 · answered Oct 06 '19 at 17:40

Since OP is a beginner, I would propose another solution that doesn't use regex

var myMessage = "Learning is fun!";
var arr1 = myMessage.split("");

function onlyLetters(array){
let arr2 = []
for(let i = 0; i < array.length; i++){
    if(isLetter(array[i])){
      arr2.push(array[i])
    }
}
   return arr2
}

function isLetter(c) {
   return c.toLowerCase() != c.toUpperCase();
}

How do I filter out a string to contain only letters in vanilla Javascript?

4 Answers4