Question

How to check if a character is letter in JavaScript

Answer 1

function isAlpha(ch) {
  if (typeof ch !== 'string') {
    	return false;
  }

  return /^[a-zA-Z]+$/.test(ch);
}

console.log(isAlpha ('z')); 
console.log(isAlpha ('8')); 
console.log(isAlpha (' ')); 
console.log(isAlpha (null)); 
console.log(isAlpha ('*'));
console.log(isAlpha ('javascript'));





/*
run:

true
false
false
false
false
true

*/

 

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Answer 2

function isAlpha(ch) {
  if (typeof ch !== 'string') {
        return false;
  }
 
  return ch.length === 1 && /^[a-zA-Z]+$/.test(ch);
}

console.log(isAlpha ('z')); 
console.log(isAlpha ('8')); 
console.log(isAlpha (' ')); 
console.log(isAlpha (null)); 
console.log(isAlpha ('*'));
console.log(isAlpha ('javascript'));





/*
run:

true
false
false
false
false
false

*/

 

70+ SQL courses for beginners and professionals

Answer 3

function isAlpha(ch) {
	 return typeof ch === "string" && ch.length === 1 && 
                (ch >= "a" && ch <= "z" || ch >= "A" && ch <= "Z");
}

console.log(isAlpha ('z')); 
console.log(isAlpha ('8')); 
console.log(isAlpha (' ')); 
console.log(isAlpha (null)); 
console.log(isAlpha ('*'));
console.log(isAlpha ('javascript'));





/*
run:

true
false
false
false
false
false

*/

 

70+ SQL courses for beginners and professionals