01.js

function whatDoesItDo(val){

    return val ? 1 : 2;

}

02.js

function whatDoesItDo(param){

    return { blue:"#0000ff", green:"#00ff00", red:"#ff0000" }[param];

}

03.js

function whatDoesItDo(color){

    if (color !== 'blue' || color !== 'green') {
        color = 'red';
    }
	
    return color;
}

04.js

function whatDoesItDo(arr){

    return arr.filter(function(elem, pos) {
        return arr.indexOf(elem) == pos;
    });

};

05.js

function whatDoesItDo(arr){
    
    return arr.reduce(function(s, n){ return s + n; }, 0);

}

06.js

function whatDoesItDo(arr){
    
    return arr.map( function(x){ return x*2; });

}

07.js

function whatDoesItDo(mood){
    
    return mood && "I like this" || "I don't like this";

}

08.js

function whatDoesItDo(str){
    
    return str.split('').reverse().join('')

}

09.js

function whatDoesItDo(){

    return document.querySelectorAll('*').length;

}

10.js

function whatDoesItDo(arr){

    return Math.max.apply(null, arr);

}

11.js

function whatDoesItDo(arr){

    return arr.slice(0).sort();

}

12.js

function whatDoesItDo(num){

    return Math.max(0, Math.min(10, num));

}

13.js

function whatDoesItDo(){

    var values = [];
    
    myBlock: {
        values.push('1');
        values.push('2');
        break myBlock;
        values.push('3');
    }
    
    values.push('4');
    
    return values.join(',');
}

14.js

function whatDoesItDo(){

    return Array(4).join("lol" - 2) + " Batman!";

}

15.js

function whatDoesItDo(str){

    return str.bold().italics();

}

16.js

function whatDoesItDo(str){

    return /^\d{3,}$/.test(str);

}

17.js

function whatDoesItDo(num){

    return this + num;

}

whatDoesItDo = whatDoesItDo.bind(10);

18.js

function whatDoesItDo(){

    return (![]+[])[+[]]+(![]+[])[+!+[]]+
           ([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]];

}