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

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/**

* @function maxCharacter

* @example - Given a string of characters, return the character that appears the most often. Example: input = "Hello World!" return "l"

* @param {string} str

* @param {RegExp} ignorePattern - ignore the char in str that is not required

* @returns {string} - char

const maxCharacter = (str, ignorePattern) => {

// initially it's count only alphabets

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

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

} else if (!str) {

throw new Error('The param should be a nonempty string')

}

// store all char in occurrence map

const occurrenceMap = new Map()

for (const char of str) {

if (!ignorePattern?.test(char)) {

occurrenceMap.set(char, occurrenceMap.get(char) + 1 || 1)

}

// find the max char from the occurrence map

let max = { char: '', occur: -Infinity }

for (const [char, occur] of occurrenceMap) {

if (occur > max.occur) {

max = { char, occur }

}

return max.char

}

export default maxCharacter