$('#starred-posts').on('hover', 'a[href$=.jpg]', function(e) { ... });

[].filter.call(document.querySelector('#starred-posts').querySelectorAll('li a'), function(a) { return a.href.match(/\.(?:jpg|png|gif)$/); });

[image link which is very very very very long] some other text

if (!$.forEach)
  $.forEach = (collection, closure) => [].slice.call(collection).forEach(closure);

// Start by checking if we have work to do - if no oneboxed pictures are in the star-script, don't waste time doing nothing.
function isOnebox(msgId) {
  $.post('/message/' + msgId, {plain: true})
    .success(response => return /^!?https?:\/\/[^ ]+\.(?:jpg|png|gif|svn)$/.test(response))
}
document.getElementById("starred-posts")
isOnebox(20859254)

function toNativePromise(jQueryPromise) {
    return new Promise(function(resolve, reject) {
        return jQueryPromise.done(resolve).fail(reject);
    });
}

function toNativePromise(jQueryPromise) {
    return new Promise(function(resolve, reject) {
        return jQueryPromise.done(resolve).fail(reject);
    });
}

function isOnebox(msgId) {
    return toNativePromise($.post(`/message/${msgId}`))
        .then(function(response) {
            return /^!?https?:\/\/[^ ]+\.(?:jpg|png|gif|svn)$/.test(response);
        });
}

isOnebox(20859254).then(console.log.bind(console));

var potentialOneboxes = [20669131, 20859254, 20859233]
Promise.all(potentialOneboxes.map(isOnebox))
    .then(console.log.bind(console));

function toNativePromise(jQueryPromise) {
    return new Promise(function(resolve, reject) {
        return jQueryPromise.done(resolve).fail(reject);
    });
}

function isOnebox(msgId) {
    return toNativePromise($.post('/message/' + msgId, {plain: true}))
        .then(function(response) {
            return /^!?https?:\/\/[^ ]+\.(?:jpg|png|gif|svn)$/.test(response);
        });
}
var potentialOneboxes = [20669131, 20859254, 20859233]
Promise.all(potentialOneboxes.map(isOnebox))
    .then(console.log.bind(console));

let foo = function() { return this.x; };
let obj = {x: 'foobar'};
let boundFoo = foo.bind(obj);

boundFoo(); // foobar

foo.call(obj); // foobar

for (let i = 0; i < 10; i++) {}
// i died here

for (var i = 0; i < 10; i++) {}
// i === 10 here