The Last Child Selector is used to select the elements, who are the last child of their parent.
Let us simplify with the below example.
<html> <head> <title> My First Programme </title> </head> <body> <h1> JQuery </h1> <div class = "newClass"> <p class = "para1"> First Paragraph </p> <p class = "para2"> Second Paragraph </p> <p class = "para3"> Third Paragraph </p> </div> <button> Click me </button> <script src = "https://cdnjs.cloudflare.com/ajax/libs/JQUERY/3.3.1/jquery.min.js"> </script> <script> $('button').click( function() { $('p:last-child').text("The last child of div element got replaced") }); </script> </body> </html>
So, if you see the above code. We can see that there are three <p> elements, those are inside a <div> element.
<div class = "newClass"> <p class = "para1"> First Paragraph </p> <p class = "para2"> Second Paragraph </p> <p class = "para3"> Third Paragraph </p> </div>
Now, if you consider the DOM,
The <div> element has three children of type <p>.
<p class = "para1"> First Paragraph </p> <p class = "para2"> Second Paragraph </p> <p class = "para3"> Third Paragraph </p>
And the last child of <div> element is,
<p class = "para3"> Third Paragraph </p>
And on button click, the contents of last element gets replaced with The last child of div element got replaced.
And this happened with the :last-child element selector.
$('button').click( function() { $('p:last-child').text("The last child of div element got replaced") });
The moment the button is clicked, JQuery statement gets triggered.
$('p:last-child').text("The last child of div element got replaced")
And the JQuery code locates the last child of <div> element and changes its contents.
Now let us take the next example, where we are taking a <span> as the last child of <div>.
<html> <head> <title> My First Programme </title> </head> <body> <h1> JQuery </h1> <div class = "newClass"> <p class = "para1"> First Paragraph </p> <p class = "para2"> Second Paragraph </p> <p class = "para3"> Third Paragraph </p> <span> My Span </span> </div> <button> Click me </button> <script src = "https://cdnjs.cloudflare.com/ajax/libs/JQUERY/3.3.1/jquery.min.js"> </script> <script> $('button').click( function() { $('p:last-child').text("The last child of div element got replaced") }); </script> </body> </html>
Now, if you see the above code, nothing actually changed on Button click.
Let us take the DOM to understand it.
And right now, the last child of <div> is a <span> and not a <p>.
<div class = "newClass"> <p class = "para1"> First Paragraph </p> <p class = "para2"> Second Paragraph </p> <p class = "para3"> Third Paragraph </p> <span> My Span </span> </div>
And since, the JQuery statement,
$('p:last-child').text("The last child of div element got replaced")
Searches for the <p> element that is the last child, it does not get it. As <p> element is the first, second and third child of <div> element.