1if(document.getElementById("myElmentID").classList.contains("hidden")){
2// I have the 'hidden' class
3}

1if (myElement.classList.contains('someClassname')) {
2    // do something
3}

1element.classList.contains('class');

1function whatIsInAName(collection, source) {
2  // "What's in a name? that which we call a rose
3  // By any other name would smell as sweet.”
4  // -- by William Shakespeare, Romeo and Juliet
5  var srcKeys = Object.keys(source);
6
7  return collection.filter(function(obj) {
8    return srcKeys.every(function(key) {
9      return obj.hasOwnProperty(key) && obj[key] === source[key];
10    });
11  });
12}
13
14// test here
15whatIsInAName(
16  [
17    { first: "Romeo", last: "Montague" },
18    { first: "Mercutio", last: null },
19    { first: "Tybalt", last: "Capulet" }
20  ],
21  { last: "Capulet" }
22);