JavaScript Introduction

JavaScript is a popular scripting language that control the behavior of the webpage using script.

Where to Place JavaScript Code?

You can place your JavaScript code in two places.

  • Inside the HTML document
  • Use an external file for JavaScript and link to HTML document.

JavaScript inside HTML page

<script>
   document.write("Hello world");
<script/>

External JavaScript File

For external JavaScript file, you have to link it to HTML document.

<script src="demo.js"></script>

Output Method in JavaScript

JavaScript programming output method in four different ways. They are listed below.

  • <mark style="background-color:rgba(0, 0, 0, 0);color:#bc1212" class="has-inline-color">document.getElementById(“demo”).innerHTML = ‘hello”;</mark>
  • <mark style="background-color:rgba(0, 0, 0, 0);color:#ba1010" class="has-inline-color">console.log(“Hello”);</mark>
  • <mark style="background-color:rgba(0, 0, 0, 0);color:#b61414" class="has-inline-color">alert(“hello”);</mark>
  • <mark style="background-color:rgba(0, 0, 0, 0);color:#b81414" class="has-inline-color">document.write(“Hello”);</mark>

The first method is using <mark style="background-color:rgba(0, 0, 0, 0);color:#b91515" class="has-inline-color">HTML DOM</mark> and <mark style="background-color:rgba(0, 0, 0, 0);color:#c70d0d" class="has-inline-color">selector API</mark> functions like <mark style="background-color:rgba(0, 0, 0, 0);color:#b01414" class="has-inline-color">getElementById</mark>, etc.

The second method prints the output to the browser console.

The third method usually used for creating error or warning for program that is displayed to users as a popup box.

The last method, is <mark style="background-color:rgba(0, 0, 0, 0);color:#bb1212" class="has-inline-color">document.write()</mark>, that simply write to the document body wiping everything out except the output.