A function to convert letters into a phone number sequence.

lettersToPhoneNumber.js

/**
 * A function to convert letters into a phone number sequence.
 * @param {string} searchStr - String of letters to convert into a phone number sequence.
 * @returns {number} The String of letters converted into phone number sequence.
 */
function lettersToPhoneNumber(searchStr) {  

    // convert lowercase string to uppercase since we compare against uppercase;
    // then split string into an array of letters;
    searchStr = searchStr.toUpperCase().split('')

    // create virtual keypad, associating alpha characters with a single digit;
    const keyPads = [{  
        alpha: ['A', 'B', 'C'],
        digit: 2 
    }, {  
        alpha: ['D', 'E', 'F'],
        digit: 3 
    }, {  
        alpha: ['G', 'H', 'I'],
        digit: 4 
    }, {  
        alpha: ['J', 'K', 'L'],
        digit: 5 
    }, {  
        alpha: ['M', 'N', 'O'],
        digit: 6 
    }, {  
        alpha: ['P', 'Q', 'R', 'S'],
        digit: 7 
    }, {  
        alpha: ['T', 'U', 'V'],
        digit: 8 
    }, {  
        alpha: ['W', 'X', 'Y', 'Z'],
        digit: 9 
    }, {
        alpha: [' '],
        digit: 0
    }]

    // declare our results as an array;
    let result = []

    // iterate over each letter of the string
    searchStr.forEach(letter => {

        // filters the virtual keypads for the current letter;
        // since we're creating a single digit array, 
        // we immediately select [0].digit to return the digit corresponding with the letter;
        let digit = keyPads.filter(keyPad => keyPad.alpha.indexOf(letter) > -1)[0].digit 

        // using the spread operator, we concatenate a new array;
        result = [ ...result,  digit] 
    })   

    // we return the numbers as a number using the Array.prototype.join method nested within parseInt;
    return parseInt(result.join(''))
}