window.fbAsyncInit = function () {
    FB.init({
        appId  : '<your Facebook app id>',
        xfbml  : true,
        version: 'v2.5'
    });
};

(function (d, s, id) {
    var js, fjs = d.getElementsByTagName(s)[0];
    if (d.getElementById(id)) {
        return;
    }
    js     = d.createElement(s);
    js.id  = id;
    js.src = "//connect.facebook.net/en_US/sdk.js";
    fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));

 FB.ui({
    method     : 'feed',
    link       : 'http://your-url-here.com',
    name       : 'Share title',
    description: 'Share description, yadda',
    picture    : 'http://image-url-here.com'
}, function (response) {

  //Do something with the response

});

//These are variables because in real life, you'll likely automatically create these elsewhere in your app.
var share_url = encodeURIComponent('http://whatever.com');
var share_text = 'Your share text with marketing speak in it, preferably.';

var url = 'http://twitter.com/share?url=' + share_url + '&text='+share_text;

function openWindow(url) {
    let winWidth, winHeight;

    winWidth  = 600;
    winHeight = 400;

    var winTop  = (screen.height / 2) - (winHeight / 2);
    var winLeft = (screen.width / 2) - (winWidth / 2);
    var w       = window.open(url, 'sharer', 'top=' + winTop + ',left=' + winLeft + ',toolbar=0,status=0,width=' + winWidth + ',height=' + winHeight);

    return (!w); // opens in new window/tab if allowed

}
    //Assuming jQuery is around, I mean, why wouldn't it be?

    $(".my-share-link").on("click", function(){

        openWindow(your_url_from_step_one);  
    });

//These are variables because in real life, you'll likely automatically create these elsewhere in your app.
var share_url = encodeURIComponent('http://whatever.com');
var share_text = 'Your share text with marketing speak in it, preferably.';
var share_title = 'Your share title';
var post_type = 'photo'; //this can be any standard tumblr post types (https://www.tumblr.com/docs/en/api/v2#posts)
var photo_url = encodeURIComponent('http://your-photo-url.com/example.jpg'); 


var tumblr_url = 'https://www.tumblr.com/widgets/share/tool?url='
+ share_url + '&posttype='
+ post_type + '&title='
+ share_title + '&caption='
+ share_text+ '&content='
+ photo_url;

$(".my-share-link").on("click", function(){

    openWindow(tumblr_url);  
});