JavaScript Fundamentals

3 minute read

Published:

This lesson covers JavaScript Fundamentals.

Java Script Fundamentals

Examples

  • Changing HTML content from java script
/* css/style.css */
h1{
    color: red;
}

input[type=submit] {
    width: 4em;
    height: 1.5em;
    font-size:2em;
}
<!-- index.html -->
<!doctype html>
<html lang="en">
    <head>
      <meta charset="utf-8" />
      <title>Hello JS</title>
      <link rel="stylesheet" href="css/style.css">
    </head>

    <body align="center">
        <h1 id="hello"></h1>
        <input type="submit" value="Hello" onclick="hello()">
        <script>
        function hello() {
          document.getElementById("hello").innerHTML = "Welcome to My First Page";
        }
        </script>
    </body>

</html>
  • Checking length of entered username
/* css/style.css */
h1{
    color: red;
}

input[type=submit] {
    width: 4em;
    height: 1.5em;
    font-size:1.5em;
}

input[type=text] {
    width: 10em;
    height: 1.5em;
    font-size:1.5em;
}
<!-- index.html -->
<!doctype html>
<html lang="en">
    <head>
      <meta charset="utf-8" />
      <title>Hello JS</title>
      <link rel="stylesheet" href="css/style.css">
    </head>

    <body align="center">
        <h1> Welcome </h1>

        <input type="text" name="username" id="username" placeholder="Enter username"> <br><br>
        <input type="submit" name="submit" id="submit" value="Submit" onclick="submit()">

        <script>
        function submit() {
          var username = document.getElementById("username").value
          var username_len = username.length
          if (username_len < 6){
              alert("you entered username of "+ username_len + " chars, it should be atleast of 6 characters");
          }
        }
        </script>
    </body>
</html>
  • JS Calculator
/* css/style.css */
h1{
    color: red;
}
p {
  font-size: 3em;
}

input[type=submit] {
    width: 5em;
    height: 1.5em;
    font-size:1.5em;
}

input[type=radio] {
  width: 1em;
  height: 2em;
  font-size:1.5em;
}

input[type=text] {
    width: 10em;
    height: 1.5em;
    font-size:1.5em;
}

input[type=number] {
    width: 15em;
    height: 1.5em;
    font-size:1.5em;
}
<!-- index.html -->
<!doctype html>
<html lang="en">
    <head>
      <meta charset="utf-8" />
      <title>Hello JS</title>
      <link rel="stylesheet" href="css/style.css">
    </head>

    <body align="center">
        <h1> JS Calculator </h1>

        <input type="number" name="num1" id="num1" placeholder="Enter first number"> <br><br>
        <input type="number" name="num2" id="num2" placeholder="Enter second number"> <br><br>

        <input type="radio" name="sign" value="addition" checked> Addition
        <input type="radio" name="sign" value="subtraction" > Subtraction
        <input type="radio" name="sign" value="multiplication"> Multiplication
        <input type="radio" name="sign" value="division" > Division

        <br><br>

        <p id="result"></p>

        <input type="submit" name="submit" id="submit" value="Compute" onclick="compute()">

        <script>

        function strip(number) {
          return (parseFloat(number).toPrecision(3));
        }

        function compute() {
          var num1 = document.getElementById("num1").value
          var num2 = document.getElementById("num2").value
          num1 = parseFloat(num1)
          num2 = parseFloat(num2)

          var sign = document.getElementsByName('sign');
          var sign_name = ""

          for(i=0; i<sign.length; i++) {
                if(sign[i].checked)
                  var sign_name = sign[i].value;
            }

          var num = ""
          if(sign_name === "addition")
            num = num1 + num2
          if(sign_name === "subtraction")
              num = num1 - num2
          if(sign_name === "multiplication")
              num = num1 * num2
          if(sign_name === "division")
            num = num1 / num2
          num = strip(num)
          document.getElementById("result").innerHTML = " Result is " + num

        }
        </script>
    </body>
</html>
  • JS Calculator using external js file
/* css/style.css */
h1{
    color: red;
}
p {
  font-size: 3em;
}

input[type=submit] {
    width: 5em;
    height: 1.5em;
    font-size:1.5em;
}

input[type=radio] {
  width: 1em;
  height: 2em;
  font-size:1.5em;
}

input[type=text] {
    width: 10em;
    height: 1.5em;
    font-size:1.5em;
}

input[type=number] {
    width: 15em;
    height: 1.5em;
    font-size:1.5em;
}
/* js/script.js */

function strip(number) {
  return (parseFloat(number).toPrecision(3));
}

function compute() {
  var num1 = document.getElementById("num1").value
  var num2 = document.getElementById("num2").value
  num1 = parseFloat(num1)
  num2 = parseFloat(num2)

  var sign = document.getElementsByName('sign');
  var sign_name = ""

  for(i=0; i<sign.length; i++) {
        if(sign[i].checked)
          var sign_name = sign[i].value;
    }

  var num = ""
  if(sign_name === "addition")
    num = num1 + num2
  if(sign_name === "subtraction")
      num = num1 - num2
  if(sign_name === "multiplication")
      num = num1 * num2
  if(sign_name === "division")
    num = num1 / num2
  num = strip(num)
  document.getElementById("result").innerHTML = " Result is " + num

}
<!-- index.html -->
<!doctype html>
<html lang="en">
    <head>
      <meta charset="utf-8" />
      <title>Hello JS</title>
      <link rel="stylesheet" href="css/style.css">
      <script src="js/script.js"></script>
    </head>

    <body align="center">
        <h1> JS Calculator </h1>

        <input type="number" name="num1" id="num1" placeholder="Enter first number"> <br><br>
        <input type="number" name="num2" id="num2" placeholder="Enter second number"> <br><br>

        <input type="radio" name="sign" value="addition" checked> Addition
        <input type="radio" name="sign" value="subtraction" > Subtraction
        <input type="radio" name="sign" value="multiplication"> Multiplication
        <input type="radio" name="sign" value="division" > Division

        <br><br>

        <p id="result"></p>

        <input type="submit" name="submit" id="submit" value="Compute" onclick="compute()">


    </body>
</html>