<button onclick="alert(‘Hello‘)">Say hello</button>

<button id="helloBtn">Say hello</button>

// Event binding using addEventListener
var helloBtn = document.getElementById("helloBtn");

helloBtn.addEventListener("click", function (event) {
    alert("Hello.");
}, false);

// Event binding using a convenience method
$("#helloBtn").click(function (event) {
    alert("Hello.");
});

// The many ways to bind events with jQuery
// Attach an event handler directly to the button using jQuery‘s
// shorthand `click` method.
$("#helloBtn").click(function (event) {
    alert("Hello.");
});

// Attach an event handler directly to the button using jQuery‘s
// `bind` method, passing it an event string of `click`
$("#helloBtn").bind("click", function (event) {
    alert("Hello.");
});

// As of jQuery 1.7, attach an event handler directly to the button
// using jQuery‘s `on` method.
$("#helloBtn").on("click", function (event) {
    alert("Hello.");
});

// As of jQuery 1.7, attach an event handler to the `body` element that
// is listening for clicks, and will respond whenever *any* button is
// clicked on the page.
$("body").on({
    click: function (event) {
        alert("Hello.");
    }
}, "button");

// An alternative to the previous example, using slightly different syntax.
$("body").on("click", "button", function (event) {
    alert("Hello.");
});