How to Check If Character Is a Letter in JavaScript

How to check if character is a letter in Javascript?

I believe this plugin has the capabilities you seek: http://xregexp.com/plugins/ (github link: https://github.com/slevithan/xregexp)

With it you can simply match all unicode letters with \p{L}.

Read the header of this source file to see which categories it supports: http://xregexp.com/plugins/xregexp-unicode-categories.js

How to check if a character is a letter or a number in javascript?

Here:

if (64 < Letter.charCodeAt(0) < 91) //...

JS isn't Python. You can't simply do a < b < c, you need to explicitly use the logical && operator: (a < b) && (b < c).

Detecting if a character is a letter

You could use a regular expression. Unfortunately, JavaScript does not consider international characters to be "word characters". But you can do it with the regular expression below:

var firstLetter = name.charAt(0);
firstLetter = firstLetter.toUpperCase();
if (!firstLetter.match(/^\wÀÈÌÒÙàèìòùÁÉÍÓÚÝáéíóúýÂÊÎÔÛâêîôûÃÑÕãñõÄËÏÖÜäëïöüçÇßØøÅåÆæÞþÐð$/)) {
    firstLetter = "0";
}
if (words[firstLetter] === undefined) {
    words[firstLetter] = [];
} 
words[firstLetter].push(name);

Check if first character of a string is a letter in JavaScript

onlyLetters.test(str) checks the whole string. To get the first character, use str.charAt(0).

function SearchingChallenge(str) {
  let onlyLetters = /^[a-zA-Z]+$/;
  if (str.length > 4 && str.length < 25) {
    if (onlyLetters.test(str.charAt(0))) {
      return true;
    } else {
      return false;
    }
  } else {
    return false;
  }
}
console.log(SearchingChallenge('Hello World!'));
console.log(SearchingChallenge('!dlroW olleH'));
console.log(SearchingChallenge('u__adced_123'));

How can I test if a letter in a string is uppercase or lowercase using JavaScript?

The answer by josh and maleki will return true on both upper and lower case if the character or the whole string is numeric. making the result a false result.
example using josh

var character = '5';
if (character == character.toUpperCase()) {
 alert ('upper case true');
}
if (character == character.toLowerCase()){
 alert ('lower case true');
}

another way is to test it first if it is numeric, else test it if upper or lower case
example

var strings = 'this iS a TeSt 523 Now!';
var i=0;
var character='';
while (i <= strings.length){
    character = strings.charAt(i);
    if (!isNaN(character * 1)){
        alert('character is numeric');
    }else{
        if (character == character.toUpperCase()) {
            alert ('upper case true');
        }
        if (character == character.toLowerCase()){
            alert ('lower case true');
        }
    }
    i++;
}

How to check if a character is within a range of characters?

Use match with a regex to return the length of the returned array where letters are not within your range.

function counter(str) {
  return str.match(/[^a-m]/g).length;
}

console.log(counter('zhuresma'));
console.log(counter('bob'));
console.log(counter('abcdefghijklmnopqrstuvwxyz'));

Check if string contains any letter (Javascript/jquery)

You have to use Regular Expression to check that :-

var regExp = /[a-zA-Z]/g;var testString = "john";            if(regExp.test(testString)){  /* do something if letters are found in your string */} else {  /* do something if letters are not found in your string */}

Javascript Function that returns true if a letter?

You could just use a case-insensitive regular expression:

var isAlpha = function(ch){
  return /^[A-Z]$/i.test(ch);
}

If you are supposed to be following the instructions in the comments about greater than and less than comparisons, and you want to check that the input is a string of length 1, then:

var isAlpha = function(ch){  return typeof ch === "string" && ch.length === 1         && (ch >= "a" && ch <= "z" || ch >= "A" && ch <= "Z");}
console.log(isAlpha("A"));      // trueconsole.log(isAlpha("a"));      // trueconsole.log(isAlpha("["));      // falseconsole.log(isAlpha("1"));      // falseconsole.log(isAlpha("ABC"));    // false because it is more than one character

How to Check If Character Is a Letter in JavaScript