What is unobtrusive javascript?

Question

How to add behavior to an element using javascript?

Answer 1

Unobtrusive JavaScript is a general approach to the use of JavaScript in web pages.

how can i add one more behavior to this using JavaScript is below

alert("say hello again");
sayGoodMorning()

Answer 2

"Unobtrusive JavaScript" is a general approach to the use of JavaScript in web pages. Though the term is not formally defined, its basic principles are generally understood to include:

1. Separation of functionality (the "behavior layer") from a Web page's structure/content and presentation
2. Best practices to avoid the problems of traditional JavaScript programming (such as browser inconsistencies and lack of scalability)
3. Progressive enhancement to support user agents that may not support advanced JavaScript functionality.

So it is basically separating behavior or javascript from presentation or html.

Example:

<input type="button" id="btn" onclick="alert('Test')" />

That is not unobstrusive javascript because behaviour and presentation are mixed. The onclick shouldn't be there in html and should be part of javascript itself not html.

With above example, you can go unobstrusive like this:

<input type="button" id="btn" />

JavaScript:

var el = document.getElementById('btn');
el.onclick = function(){
  alert('Test');
};

That time we have separated javascript from html with a very basic example.