Use map in JavaScript

I can't really understang what the problem is, but I made a jsFiddle to show how to put the value of the return into a div:
jsFiddle http://jsfiddle.net/5v3M5/1/

var a = get();
document.getElementById('return').innerHTML = a;

Not sure really what the expectation is - but if you just want to see if the property exists in the javascript object (map) you can just do this -

if(map.key1)
{
  // do what has to be done if the key exists
}

or in your case - you can simply use a ternary operator

return (map.key1 ? "hello" : "kirti"); 

The 'in' operator you are using will not work with 'if' as it is used to loop through all the properties of the object - more about for..in here

Try this:

var map = {'key1': 'value1', 'key2': 'value2'};
for (var key in map) {
    if(key == 'key1'){
        return 'hello';
    } else {
        return 'kirti';
    }
}

If you have html like this :

Button : <input id="bt" type="button" value="BUTTON">

You can use jquery and the alert() function to show the result :

    $(document).ready(function(){
        $('#bt').on('click', function(){
            alert(get());
        });
    }); 

function get(){
var map = {'key1': 'value1', 'key2': 'value2'};
if ('key1' in map) {
   alert('hello');
} else {
    alert('kirti');
}

}