Javascript Letter Frequency Analyzer.

letter-frequency.js

// Takes an array of characters or a string
function analyze(input){
    var chars = undefined;
    var obj = {};    
    if(input instanceof Array){
        chars = input;
    } else if(typeof input === 'string' || input instanceof String) {
        chars = input.split("");
    } else return null;
    
    for(var i = 0; i < chars.length; i++) {
        if(!obj[chars[i]]) obj[chars[i]] = {frequency: 1};        
        else  obj[chars[i]].frequency = obj[chars[i]].frequency + 1;
    }

    for (var key in obj) {
        if (obj.hasOwnProperty(key)) {
            obj[key].percentage = (obj[key].frequency / chars.length) * 100;
        }
    }

    return obj;
}