Sandbox::https://github.com/sibalonecoding-code/JavaScript/blob/master/String/CountLetters.js

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/**

* @function countLetters

* @description Given a string, count the number of each letter.

* @param {String} str - The input string

* @return {Object} - Object with letters and number of times

* @example countLetters("hello") => {h: 1, e: 1, l: 2, o: 1}

const countLetters = (str) => {

const specialChars = /\W/g

if (typeof str !== 'string') {

throw new TypeError('Input should be a string')

}

if (specialChars.test(str)) {

throw new TypeError('Input must not contain special characters')

}

if (/\d/.test(str)) {

throw new TypeError('Input must not contain numbers')

}

const obj = {}

for (let i = 0; i < str.toLowerCase().length; i++) {

const char = str.toLowerCase().charAt(i)

obj[char] = (obj[char] || 0) + 1

}

return obj

}

export { countLetters }