Q:

Enabling the Search button when the user types or makes a selection

I'd like to write some sort of function that would allow functionality to be added to enable the "Search" button when the user has either:

made a selection in either of the select boxes 
or has typed a value into one of the input boxes on the page

Vice-versa, if either of the select or input boxes are empty, then disable the search button.
I apologize in advance and would like to say that I am newcomer to JavaScript and I am not sure where to begin, other examples on the web are confusing to me and do not seem to fit my needs.
Here is the HTML Markup:
<!DOCTYPE html>
<html>
    <head>
    </head>
    <body>
        Cars
        <select id="car">
            <option value=""></option>
            <option value="volvo">Volvo</option>
            <option value="saab">Saab</option>
            <option value="mercedes">Mercedes</option>
            <option value="audi">Audi</option>
        </select>
        <br><br>

        Fruits
        <select id="fruits">
            <option value=""></option>
            <option value="apple">apple</option>
            <option value="banana">banana</option>
            <option value="pear">pear</option>
            <option value="strawberry">strawberry</option>
            <option value="mango">mango</option>
            <option value="orange">orange</option>
        </select>
        <br><br>

        Vegetable
        <input type="input" id="veggie">
        <br><br>

        Number
        <input type="input" id="number">
        <br><br>

        <input type="button" value="search" disabled>
    </body>
</html>

A:

You should use the jQuery change() function, like this:
$("select#fruits").change(function(){
   $('input[type="button"]').removeClass("disabled");
});

Give your input the disabled class which disables the button like:
.disabled{
     pointer-events: none;
}

The upper code removes this class when someone is selecting something at your select input.
UPDATE: 
$("select#fruits").change(function(){
    $("input[type="button"]").removeAttr("disabled");
});

This removes the "disabled" attribute for your button.

