如何使用JavaScript更改类的背景颜色？

Question

I am trying to use javaScript to change the background colour of my class which is called row, My javascript and html code is listed below but its not working and im not sure what the problem is, any help would be greatly appreciated.

function changeColour() {
    var row = document.getElementsByClassName("row");
    row.style.backgroundColor="black";
}

My html code for the button is listed below.

<input type="button" id="btnColour" value="Change Colour" 
onclick="changeColour();" />

Answer 1

getElementsByClassName returns a nodeList , an array-like object filled with the matching elements, you have to iterate over that nodeList and set the style on each matching element

function changeColour() {

    var row = document.getElementsByClassName("row");

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

}