How to convert letters to numbers with Javascript?

Question

How could I convert a letter to its corresponding number in JavaScript?

For example:

a = 0
b = 1
c = 2
d = 3

I found this question on converting numbers to letters beyond the 26 character alphabet, but it is asking for the opposite.

Is there a way to do this without a huge array?

Right, but why `A`? why not `'a'` some other character? Also, are all the characters ASCII? — mgilson, Mar 25 '14 at 02:32
@mgilson - Sorry, should be lower case. The characters are just a string variable that I am trying to convert. — Fizzix, Mar 25 '14 at 02:34

Ry- · Accepted Answer · 2015-06-22T22:34:58.900

154

You can get a codepoint* from any index in a string using String.prototype.charCodeAt. If your string is a single character, you’ll want index 0, and the code for a is 97 (easily obtained from JavaScript as 'a'.charCodeAt(0)), so you can just do:

s.charCodeAt(0) - 97

And in case you wanted to go the other way around, String.fromCharCode takes Unicode codepoints* and returns a string.

String.fromCharCode(97 + n)

* not quite

edited Jun 22 '15 at 22:34

answered Mar 25 '14 at 02:35

Ry-

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Where is `n` coming from? – Fizzix Mar 25 '14 at 02:37
4

@fizzix from... you. You specify `n`. You can do a loop 0 to 25 if you want to auto-pop an array or w/e – CrayonViolent Mar 25 '14 at 02:38
So `n` could be found from `myLetter.charCodeAt(0)`? – Fizzix Mar 25 '14 at 02:40
@fizzix, you said you wanted to convert a number to its corresponding letter, so `n` would be that number. `String.fromCharCode(97 + 3) === 'c'`, e.g.. – Ry- Mar 25 '14 at 02:41
@minitech - I am extremely sorry, but it seems as if I typed it the wrong way round in the description to what it is in the title. Read my edit. Sorry. – Fizzix Mar 25 '14 at 02:43
1

@fizzix: Then it would be `c.charCodeAt(0) - 97`. =) – Ry- Mar 25 '14 at 02:49
make sure to lowercase the letter – Kevin Jantzer Dec 12 '17 at 23:45

score 19 · Answer 2 · answered Dec 08 '16 at 21:21

19

This is short, and supports uppercase and lowercase.

const alphaVal = (s) => s.toLowerCase().charCodeAt(0) - 97 + 1

answered Dec 08 '16 at 21:21

ThomasReggi

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Why not just `const alphaVal = (s) => s.toLowerCase().charCodeAt(0) - 96` – Anthony To Apr 26 '19 at 00:55
Some answers have 97, why 96? – Toivo Säwén Mar 30 '20 at 16:45
2

@ToivoSäwén if you want a to be assigned to 1 then use 96, if you want a to be assigned to 0 then use 97. – Alex Dunlop Feb 08 '21 at 23:34

score 18 · Answer 3 · answered Mar 25 '14 at 02:55

18

Sorry, I thought it was to go the other way.

Try this instead:

var str = "A";
var n = str.charCodeAt(0) - 65;

answered Mar 25 '14 at 02:55

Matt Eno

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use " - 97" instead of " -65" for a lower case "a" to equal 0 – Matt Eno Mar 25 '14 at 03:02

KyleMit · Answer 4 · 2023-01-16T15:22:37.577

If you want to be able to handle Excel like letters past 26 like AA then you can use the following function adapted from Count with A, B, C, D instead of 0, 1, 2, 3, ... with JavaScript:

function convertLetterToNumber(str) {
  const start = 96 // "a".charCodeAt(0) - 1
  const len = str.length;
  const out = [...str.toLowerCase()].reduce((out, char, pos) => {
      const val = char.charCodeAt(0) - start
      const pow = Math.pow(26, len - pos - 1);
      return out + val * pow
  }, 0)
  return out;
}

const testCases = ["A","B","C","Z","AA","AB","BY"];
const converted = testCases.map(convertLetterToNumber);
console.log(converted); // [1,2,3,26,27,28,77]

Demo in Stack Snippets:

function convertLetterToNumber(str) {
  const start = 96 // "a".charCodeAt(0) - 1
  const len = str.length;
  const out = [...str.toLowerCase()].reduce((out, char, pos) => {
      const val = char.charCodeAt(0) - start
      const pow = Math.pow(26, len - pos - 1);
      return out + val * pow
  }, 0)
  return out;
}

const testCases = ["A","B","C","Z","AA","AB","BY"];
const converted = testCases.map(convertLetterToNumber);
console.log(converted); // [1,2,3,26,27,28,77]

score 6 · Answer 5 · answered Sep 04 '16 at 03:44

You can make an object that maps the values:

function letterValue(str){
    var anum={
        a: 1, b: 2, c: 3, d: 4, e: 5, f: 6, g: 7, h: 8, i: 9, j: 10, k: 11, 
        l: 12, m: 13, n: 14,o: 15, p: 16, q: 17, r: 18, s: 19, t: 20, 
        u: 21, v: 22, w: 23, x: 24, y: 25, z: 26
    }
    if(str.length== 1) return anum[str] || ' ';
    return str.split('').map(letterValue);
}

letterValue('zoo') returns: (Array) [26,15,15] ;

letterValue('z') returns: (Number) 26

kennebec · Answer 6 · 2014-03-25T03:27:31.703

You might assign 1 to 'a', instead of 0, to make it easy to skip (or include) punctuation, numbers or capital letters.

function a1(txt, literal){
    if(!literal) txt= txt.toLowerCase();
    return txt.split('').map(function(c){
        return 'abcdefghijklmnopqrstuvwxyz'.indexOf(c)+1 || (literal? c: '');
    }).join(' ');
}

var str= 'Hello again, world!';

/*  a1(str,'literal')>>value: (String)
H 5 12 12 15   1 7 1 9 14 ,   23 15 18 12 4 !
*/


/*  a1(str) >>value: (String)
8 5 12 12 15  1 7 1 9 14   23 15 18 12 4 
*/

Messiah Jesus Slave of RAHMAN · Answer 7 · 2020-04-13T23:15:10.840

You can use this numerical value calculator-it adds up all letter values- for any string (Not Case Sensitive):

function getSum(total,num) {return total + num};
function val(yazı,harf,değer){ rgxp = new RegExp(değer,'gim'); text = yazı.toLowerCase();
if (text.indexOf(harf) > -1){ sonuc = text.split(harf).join(değer).match(rgxp).map(Number).reduce(getSum) }else{ sonuc=0 };
return sonuc;}

String.prototype.abjad = function() {
a = val(this,'a','1'); b = val(this,'b','2'); c = val(this,'c','3'); ç = val(this,'ç','4'); d = val(this,'d','5');
e = val(this,'e','6'); f = val(this,'f','7'); g = val(this,'g','8'); ğ = val(this,'ğ','9'); h = val(this,'h','10');
ı = val(this,'ı','11'); i = val(this,'i','12'); j = val(this,'j','13'); k = val(this,'k','14'); l = val(this,'l','15');
m = val(this,'m','16'); n = val(this,'n','17'); o = val(this,'o','18'); ö = val(this,'ö','19'); p = val(this,'p','20');
r = val(this,'r','21'); s = val(this,'s','22'); ş = val(this,'ş','23'); t = val(this,'t','24'); u = val(this,'u','25');
ü = val(this,'ü','26'); v = val(this,'v','27'); y = val(this,'y','28'); z = val(this,'z','29');
return a+b+c+ç+d+e+f+g+ğ+h+ı+i+j+k+l+m+n+o+ö+p+r+s+ş+t+u+ü+v+y+z
};

Ask();
function Ask() {
    text = prompt("Please enter your text");
    if (text != null) {
    alert("Gematrical value is: " + text.abjad())
    document.getElementById("result").innerHTML = text.abjad();
    }
}

Gematrical value is: <p id="result"></p>

https://jsfiddle.net/nonidentified/0xydecze/1/

score 0 · Answer 8 · answered Jul 19 '20 at 08:33

0

I used:

let a = 'dev';
let encode = '';
for (let i = 0; i < a.length; i++) {
  let x = a.slice(i, i+1);
  encode += x.charCodeAt(0);
  
}
console.log(encode);

And result return: 100101118

answered Jul 19 '20 at 08:33

Thức Trần

109
1
5

Akash Edake · Answer 9 · 2022-11-30T15:33:29.547

function convertLetterToNumber(str) {
  if ((typeof str === "string" || str instanceof String) && /^[a-zA-Z]+$/.test(str)) {
    str = str.toUpperCase();
    let out = 0,
      len = str.length;
    for (pos = 0; pos < len; pos++) {
      out += (str.charCodeAt(pos) - 64) * Math.pow(26, len - pos - 1);
    }
    return out;
  } else {
    return undefined;
  }
}
let speling = prompt("Please enter your value", "ZZ");
let result=convertLetterToNumber(speling);
alert(result)

How to convert letters to numbers with Javascript?

9 Answers9

Demo in Stack Snippets:

Linked

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