Implementation of the algorithm solving a quadratic equation in JavaScript

<<algorithm

<!DOCTYPE html>
<html>
<body>
<script>

function linear(a,b) {
  if (a==0)
    if (b==0)
      alert("Identity equation");
    else
      alert("Contrary equation");
  else {
    var x = -b / a;
    alert("x = " + x);
  }
}

var a=prompt("a:", "");
var b=prompt("b:", "");
var c=prompt("c:", "");
if (a == 0) 
  liniowe(b,c);
else {
  var delta = b*b-4*a*c;
  if (delta < 0)
    alert("Lack of solutions");
  else 
    if (delta == 0) {
      var x = -b / (2 * a);
      alert("One solution x = " + x);
    }
    else {
      var x1 = (-b + Math.sqrt(delta)) / (2 * a);
      var x2 = (-b - Math.sqrt(delta)) / (2 * a);
      alert("x1 = " + x1 + "    x2 = " + x2);
    }
}

</script> 
</body>
</html>

Program line	Description	Algorithm block
1	In the 1st line of the program, we inform the browser that our document was written in HTML (more precisely, it is a header specific to HTML 5). Line 2 contains the <html> tag that begins the HTML code. The 3rd line starts the <body> section of our document, containing the elements that are to appear on the page. In our example, the <body> section contains only a script written in JavaScript that implements the algorithm for solving a quadratic equation. The <script> tag on line 4 informs about the start of the script.	-
6 - 16	We define the function linear that implements an algorithm for solving a linear equation.	4
18-20	We declare the variables a,b,c using the var keyword. At the same time, the assignment operator ("=") initializes these variables with user-entered values using the prompt() statement. prompt - JavaScript standard function - displays a text input pop-up on the screen. The first argument of the function specifies the text displayed as a prompt, the second is the default value entered in the edit field. As a result, the prompt() function returns the text entered by the user into the edit field and then confirmed with the OK button.	2
21	We check if the coefficient a is equal to 0. If so, we are dealing with a linear equation.	3
22	We will be in this line only when a = 0, i.e. when the equation is a linear equation. We call the function linear(b, c), which performs the algorithm for solving a linear equation. It is worth noting that the coefficient to the first power of x is denoted by b, and the intercept is c (traditionally, a and b are used respectively in a linear equation).	4
23	else, i.e. in the opposite case. At this point, the solution of the equation begins when a ≠ 0, i.e. when we are actually dealing with a quadratic equation.	-
24	We declare a delta variable and calculate its value.	5
25	We check if delta < 0.	6
26	When delta < 0, we use the alert() function to print an appropriate message informing about the lack of solutions.	7
27	This is where the program block starts when delta is not lower than zero, i.e. when the equation has solutions (one or two).	-
28	We check if delta = 0.	8
29	We calculate and save in the variable x the solution of the equation (one double - delta = 0).	9
30	We display the calculated result.	10
32	We start the program block executed when the delta = 0 condition was not met (and the earlier delta < 0 and a ≠ 0).	-
33 - 34	We calculate the solutions and assign their values to x1 and x2 variables, which are also declared using the var instruction.	11
35	We display the calculated result - two solutions of the quadratic equation.	12
46-37	We close blocks of compound statements.	-
39-41	We close the tags </script>, </body> i </html>.	-