Introduction to JavaScript

Using Math PI & Sqrt

Enter the radius of a circle:

<FORM>
     Enter the radius of a circle: <INPUT TYPE="text" NAME="number" VALUE="25">
     <INPUT TYPE="button" VALUE="Find the circumference"
       onClick="form.result1.value = 2 * Math.PI * form.number.value">
     <INPUT TYPE="text" NAME="result1">
     <INPUT TYPE="button" VALUE="Find the square root of the first number"
       onClick="form.result2.value = Math.sqrt(form.number.value)">
     <INPUT TYPE="text" NAME="result2">
</FORM>

NOTES:

  1. A form element named abc can be accessed through JavaScript as form.abc (if the form is given a name, say "stuff" in the <FORM> tag, this name can also be used to access a form element, e.g., stuff.abc.
  1. The value of some elements, for example of text input elements, can not only be accessed but also changed via form.abc.value.
  1. <INPUT TYPE="button" VALUE="Find the circumference"
      onClick="form.result1.value = 2 * Math.PI * form.number.value">
    adds a button form element to the form. When the button is clicked JavaScript takes the value in the form element named "number" (i.e., form.number.value) and multiples that number by 2 and Math.PI - giving us the circumference of a circle. This is then assigned to form.result1.value, setting the value of the "result1" element (input box) in the form.
  1. When the 2nd button is clicked JavaScript takes the value in the form element named "number" (i.e., form.number.value) and passes that number to Math.sqrt. The value returned is just the square root of the argument. This is then assigned to form.result2.value, setting the value of the "result2" element (input box) in the form.

When a number may be entered into the form's "number" element and one of the buttons is pressed, the number's square root or circumference is calculated, depending on which button is pressed. The results of the calculation are displayed in the form's "result1" element or the form's "result2" element depending on which button is clicked.