如果一个类包含某个名称，请更改该元素的样式

Question

What I currently have in my JS file:

if (documentElement.className("child") != -1){
    documentElement.className("child").backgroundColor="red";
}

Basically as the title implies, I want all the classes with the name "child" on the page to change their background color to red.

Answer 1

className returns a string with all of the classes on the element. You need to see if that string contains your class:

if (documentElement.className.indexOf("child") != -1){

Use indexOf

Answer 2

Regarding what @Roberrrt said - you can achieve this simply selecting the 'child class' and applying a style to it.

For a visual example.

http://codepen.io/anon/pen/GNMJjr

In your code:

documentElement.className("child").backgroundColor="red";

That wouldn't work, this is a better way of achieving what you want:

document.querySelector('.child').style.backgroundColor = "red";

I still recommend using CSS. This is redundant and extremely verbose.

Answer 3

Try this maybe (tested on about:blank page with 5 <div> with 2 of them with the class="red" :

var red = [];
red = document.querySelectorAll(".red");

for (var i = 0; i < red.length; i += 1) {
     red[i].style.backgroundColor = "red";
}

If you really want to verify if the class name contains a string, use classList.contains (it often have resolved this kind of problem for me, check the MDN page )