Add style class and js style class in js

Add style class and js style class in js

Looking at js recently, it is king to lay a solid foundation. The underlying things cannot be ignored.
Adding style names in Js makes it easy to add and remove styles when using jQuery. But how to deal with js? I just read an article, cainiao-level "Seven details for beginners of JavaScript", original article address
There is a paragraph in the http://developer.51cto.com/art/201101/242546_2.htm to write such a thing: Modify the style name, I made a little extension.

I,

function addclass(elm,newclass){  var c = elm.className;  if(c!="")  elm.className=newclass;}

Write a function and pass in the object element and style name to determine whether it is empty. If it is not empty, assign a style name;

II,

function addclass(elm,newclass){  var c = elm.className;  elm.className = (c =="") ? newclass : c+' '+newclass;}

Write a function, input the object element, and add it to the style name to determine whether it is null. If it is null, assign a value. Otherwise, add a space and assign a value;

III,

function addclass(elm,newclass){   var classes = elm.className.split(' ');   classes.push(newclass);   elm.className = classes.join(' '); }

Input the object element and style name, and then set elm. className is a string separated by a space. It is removed from the space and converted into an array using the split method. Then, the style is added to the Array Using the push method, it is a very unique and awesome method to add spaces to join and convert them into strings and then assign values to the class of the element.

However, I think it is a bit inadequate. What should I do if the element already has a newclass name? Like this:

Then I want to add a div2 class to this div. If the third method is used, although there will be no errors, the page will become like this, so I use the fourth method: ** 4 ,**

function zhen(obj,claName){  var cla=obj.className.split(" ");  for(var i=0;i<cla.length;i++)  {    if(cla[i]==claName)    return;  }  cla.push(claName);  obj.className=cla.join(" ");}

Based on the advantages of the third method, a circular decision is made to ensure that no duplicate names exist.