div class="container">
    <h1>Weather App</h1>
    <form action="index.php" method="post">
        <div class="form-group">
            <label for="city" > Location</label>
            <div id="errorCity"></div>
            <input type="text" name="city" class="form-control"><br>
            <label for="temp">Temperature: </label>
            <input type="radio" name="temp" value="imperial"> F
            <input type="radio" name="temp" value="metric" checked> C <br>
            <hr>
            <button onclick="validateForm()" name="submit">Submit</button>
        </div>
    </form>
</div>

<script>
function validateForm(){
    var cityField = document.getElementById('city').value;
    var cityInput = document.getElementById('errorCity').innerHTML;

    if(cityField === ""){
        cityInput  = "Please enter a location";
        console.log(cityInput);
        return false;
    }

return true
}
</script>