The :nth-child(n) Selector is used to select the elements, who are the 'n'th 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:nth-child(2)').text("The second 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 second child of <div> element is,
<p class = "para2"> Second Paragraph </p>
And on button click, the contents of first element gets replaced with The second child of div element got replaced.
And this happened with the :nth-child(2) element selector.
$('button').click( function() { $('p:nth-child(2)').text("The second child of div element got replaced") });
The moment the button is clicked, JQuery statement gets triggered.
$('p:nth-child(2)').text("The second child of div element got replaced")
And the JQuery code locates the second child of <div> element and changes its contents.