Question

How to check if a character is letter in TypeScript

Answer 1

function isAlpha(ch : any) : any {
    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 ('typescript'));
  
  
  
  
  
/*
run:
  
true
false
false
false
false
true
  
*/

 

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Answer 2

function isAlpha(ch : any) : any {
    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 ('typescript'));
 
 
 
 
 
/*
run:
 
true
false
false
false
false
false
 
*/

 

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Answer 3

function isAlpha(ch : any) : any {
    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 ('typescript'));
  
  
  
  
  
/*
run:
  
true
false
false
false
false
false 
  
*/

 

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