Finding duplicates in JavaScript array of strings

findDupesInJsArray.js

// Some sample data
var image1 = { name: 'google1', ext: 'jpg', url: '/some/url.jpg', tags: ['red', 'pants', 'jeans'] };
var image2 = { name: 'apple5', ext: 'png', url: '/some/url.png', tags: ['red', 'black', 'jeans'] };
var image3 = { name: 'nexus7', ext: 'png', url: '/some/url.png', tags: ['black', 'pants', 'jeans', 'jeans'] };

// Tags for an image can have NO duplicate tags
image1.tags = _.uniq(image1.tags); image2.tags = _.uniq(image2.tags); image3.tags = _.uniq(image3.tags);

var images = [];
images.push(image1); images.push(image2); images.push(image3);

// Array has duplicates, which is ok
// i.e.--> ["red", "pants", "jeans", "red", "black", "jeans", "black", "pants", "jeans"]
var allTags = [];
for (var i=0; i<images.length; i++) {
  var image = images[i];
  for (var j=0; j<image.tags.length; j++) {
    allTags.push(image.tags[j]);
  }
}

var cached = {}; // Used to know if we have already added the tab
var duplicatedTags = [];
for (var i=0;i<allTags.length; i++) {
  if (cached[allTags[i]] == undefined) {
    
    // If undefined, then it's safe to add. It hasn't been added before
    cached[allTags[i]] = allTags[i];
    
    if (hasDup(allTags, allTags[i], allTags.length)) {
      duplicatedTags.push(allTags[i]);
    }
    
  }
}

// duplicatedTags now contains ["jeans"]
// You know that the 3 images you selected to edit tags all contain 'jeans' as a tag
console.log(duplicatedTags);

// arr - source array that contains all our data
// val - the value we are checking for dupes i.e. 'pants', 'shirts'
// greaterThan - this is the amount that has to be duplicated for the value to be recorded
// i.e. if 3 images are selected, then this would be 3. 3 images need to have the same tag
function hasDup(arr, val, greaterThan) {
  
    // Count for 1 item (tag)
    var count = 0;
    
    for (var i = 0; i < arr.length; i++) {
        // Every time a match is found we increment our count that will say how many exist
        if (arr[i] == val)
            count++;
    }
    
    // You have to have as many duplicates as images so the tag exists in all of them
    if (count >= greaterThan){
        return true;
    }
    
    return false;
}