Adding External JavaScript code in HTML

Its quite familiar that JavaScript need HTML to run .So there are 2 ways in incorporating Java Script in HTML

1. Adding Internally
1. adding a java script code in html code and save it as file-name.html and run it
2. Adding Externally 
1. Calling a java-script code [.js file] in your HTML code

    

 Here samp.js will be having the code to display the text when the button is clicked