I am pretty new to JavaScript, and put together a weather application. I'd like to get some feedback on improvements I could make to the code itself and also possible ways to speed up weather data display.This is a screenshot of the working site:The basics for how the application works:It checks if local storage has units set, there are 2 options, imperial and metric. If units doesn't exist, a default unit is picked based upon the browser's language settings. If a unit is set, then the application will use that. You can set the units via buttons on the page.The application uses geolocation to get the user's coordinates, and generate a link to a json file from open weather map. I then use jsonp to grab the weather data and stick it into local storage as a cache.I add a timestamp to local storage.The local storage weather data is parsed and displayed on the page. If the data is older than 30 minutes, it gets downloaded again and the cache is updated.Here is the HTML for the site:<!DOCTYPE html>    <html>        <head>            <meta charset=utf-8>            <title>Local Weather</title>            <meta description content=Get your Local weather using geolocation.>            <meta name=viewport content=width=device-width, initial-scale=1>            <link rel=stylesheet type=text/css href=//cdnjs.cloudflare.com/ajax/libs/normalize/3.0.1/normalize.min.css>            <link rel=stylesheet type=text/css href=//fonts.googleapis.com/css?family=Arimo:400,700>            <link rel=stylesheet type=text/css href=assets/style.css>            <!--[if lt IE 9]>                <script src=http://html5shiv.googlecode.com/svn/trunk/html5.js></script>            <![endif]-->        </head>        <body>            <form id=toggle>                <button type=button id=cel class=inactive onclick=SetCelsius();>&deg;C</button>                <button type=button id=far class=inactive onclick=SetFahrenheit();>&deg;F</button>            </form>            <article>                <section id=weather>                    <img alt=loading id=spinner src=assets/spinner.gif>                </section>                <section id=forecast>                    <noscript>This application requires JavaScript to function. Please enable scripts in your browser.</noscript>                </section>            </article>            <script src=//cdnjs.cloudflare.com/ajax/libs/jquery/1.9.1/jquery.min.js></script>            <script src=assets/weather.js></script>        </body>    </html>Here is the JavaScript:$(function SetUnits () {    switch (localStorage.getItem(Units)) {        case null:            if (window.navigator.language == en-US) {                localStorage.Units = imperial;                $(#far).removeClass(inactive);                $(#far).addClass(active);            }            else {                localStorage.Units = metric;                $(#cel).removeClass(inactive);                $(#cel).addClass(active);            }            break;        case metric:            $(#cel).removeClass(inactive);            $(#cel).addClass(active);            break;        case imperial:            $(#far).removeClass(inactive);            $(#far).addClass(active);            break;    }});function SetCelsius(){    localStorage.Units = metric;    $(#cel).removeClass(inactive);    $(#cel).addClass(active);    $(#far).removeClass(active);    $(#far).addClass(inactive);    location.reload();}function SetFahrenheit() {    localStorage.Units = imperial;    $(#far).removeClass(inactive);    $(#far).addClass(active);    $(#cel).removeClass(active);    $(#cel).addClass(inactive);    location.reload();}$(function geolocation (){    if (navigator.geolocation){        navigator.geolocation.getCurrentPosition(getcoordinates,showError);    }    else {        $(#weather).html(Geolocation is not supported by this browser.);    }});function getcoordinates(position) {    var lat=position.coords.latitude;    var long=position.coords.longitude;    var units=localStorage.getItem(Units);    var CurrentWeatherURL = http://api.openweathermap.org/data/2.5/weather?lat=+lat+&lon=+long+&units=+units;    var DailyForecastURL = http://api.openweathermap.org/data/2.5/forecast/daily?lat=+lat+&lon=+long+&units=+units+&cnt=1;    if (units == imperial) {        getWeather(CurrentWeatherURL, DailyForecastURL, F, mph)    }    else {        getWeather(CurrentWeatherURL, DailyForecastURL, C, m\/s)    }}function showError(error) {    switch(error.code) {        case error.PERMISSION_DENIED:            $(#weather).html(User denied the request for Geolocation.);            break;        case error.POSITION_UNAVAILABLE:            $(#weather).html(Location information is unavailable.);            break;        case error.TIMEOUT:            $(#weather).html(The request to get user location timed out.);            break;        case error.UNKNOWN_ERROR:            $(#weather).html(An unknown error occurred.);            break;    }}var data_timestamp=Math.round(new Date().getTime() / 1000);function getWeather(data_url, forecast_url, temp, wind) {    $.ajax ({        url: data_url,        type: 'GET',        cache: false,        dataType: jsonp,        success: function(data) {            localStorage.WeatherCache = JSON.stringify(data);        },        error: function (errorData) {            $(#weather).html(Error retrieving current weather data :: + errorData.status);        }    });    $.ajax ({        url: forecast_url,        type: 'GET',        cache: false,        datatype: jsonp,        success: function(data) {            localStorage.ForecastCache = JSON.stringify(data);            displayData(temp, wind);        },        error: function (errorData) {            $(#forecast).html(Error retrieving forecast data :: + errorData.status);        }    });    localStorage.timestamp = data_timestamp;};function displayData(temp_units, wind_units) {    try {        // If the timestamp is newer  than 30 minutes, parse data from cache        if ( localStorage.getItem('timestamp') > data_timestamp - 1800){            var data = JSON.parse(localStorage.WeatherCache);            var forecast = JSON.parse(localStorage.ForecastCache);            document.body.style.background = url('assets/backgrounds/ +data.weather[0].icon+ .jpg') no-repeat fixed 50% 50%;            document.body.style.backgroundSize = cover;            $(#weather).html('<h2>' + data.name + '</h2><img class=icon src=assets/icons/'+data.weather[0].icon+'.png><span id=temp>'+ data.main.temp + ' </span><span id=units>&deg;'+temp_units+'</span><p id=description>'+ data.weather[0].description + '</p><p><span id=humidity>'+ data.main.humidity + '% humidity</span>&nbsp;&nbsp;&nbsp;&nbsp;'+ Math.round(data.wind.speed) + wind_units +' wind</p>');            $(#forecast).html('<p id=daily>Today\'s Forecast: '+forecast.list[0].weather[0].main+'</p><p>max: '+Math.round(forecast.list[0].temp.max)+'&deg;'+temp_units+' &nbsp;&nbsp;&nbsp;&nbsp;min: ' +Math.round(forecast.list[0].temp.min)+'&deg;'+temp_units+'</p>');        }        else {            geolocation ();        }    }    catch(error){        window.console && console.error(error);    }}I have this entire project on GitHub here.The live site is here.
JavaScript Weather App
javascript;beginner;json;api
Some parts of your code are extremely repetitive.I also wonder about reloading the page upon switching units, since you could surely just convert them in-place.In your first block, what if (somehow) the value in your localStorage is set, but not to metric or imperial? Your application probably (didn't look too deeply) won't load.Your unit conversions don't actually work. (Does this qualify for a flag for off-topic?)You're missing a quote in your meta charset.I wrote a fiddle. You can see the full version here. Here's a summary of changes:I made inactive the default styling, instead of a class.I DRYed up the system selection.I changed localStorage to use the API instead of direct assignment.I moved the event handlers into the script to separate them from the structure.I made temperatures auto-convert when changing units.I got rid of the &nbsp;s and replaced it with some styling.There may have been some changes that I left out.