/**

* @method getDomCounts - Get the tag information in some page;

* @param

* @return An object with the result of tag name as key and tag counts for value.

*/

function getDomCounts() {

let nodes = document.getElementsByTagName('*');

let tags = {};

for (let i = nodes.length - 1; i; i--) {

var tagName = nodes[i].tagName.toLowerCase();

if (tags[tagName]) {

tags[tagName]++;

} else {

tags[tagName] = 1;

}

}

return tags;

}

/**

* @method sortTags - sort an object by value of an object;

* @param tagsInfo - an object which needs to be sorted;

* @return An Array composed by the object key

*/

function sortTags(tagsInfo) {

return Object.keys(tagsInfo).sort((a,b)=> {

return tagsInfo[b]-tagsInfo[a]

})

}

let tagsInfo = getDomCounts();

let sortedTags = sortTags(tagsInfo);

let mostUsedTags= {};

for (let i = 0; i < 3; i++) {

let key = sortedTags[i];

mostUsedTags[key] = tagsInfo[key]

}

console.log(mostUsedTags);