12_01_15_solution_1.js

function countLetters(input) {
    
    // a place to store the counters
    var counters = {};
    // get the length of the input string
    
    input = input.toLowerCase();
    
    // iterate over the chars of the string
    for (var i = 0; i < input.length; i++) {
        // check to see if a letter
    
        if(input[i] <= 'z' && input[i] >= 'a') {
            // convert the char to lowercase - str.toLowerCase();
            if(counters.hasOwnProperty(input[i])) {
                // increment counter for given char obj[char]++
                counters[input[i]]++;
            }
            else {
                counters[input[i]] = 1;
            }
        }
    }
    
    // print out the char counts
    console.log(JSON.stringify(counters));
}

countLetters("The quick brown fox jumps over the lazy dog and the sleeping cat early in the day.");