JavaScript window.alert not working

Question

I recently began learning JavaScript and decided to create a program to factor quadratic functions. The program itself is longer, and takes three users inputs (secondnum,firstnum,thirdnum) representing a,b,c in the standard form ax^2+bx+c. The program functions normally until this block of code.

function discriminant(secondnum,firstnum,thirdnum) {
    var disc = Math.sqrt(Math.power(secondnum,2)-(4*firstnum*thirdnum));
    return disc;
}
ans1 = ((-1*secondnum) + disc)/(2*firstnum);
ans2 = ((-1*secondnum) - disc)/(2*firstnum);
window.alert(ans1);
window.alert(ans2);

My intention of this code is creating a function which solves for the discriminant, then uses the discriminant in the quadratic formula. I believe there is something incorrect about the discriminant function. Is this the proper way to use user input in the function? I hope this question is not too specific.

Also if it matters here is an example of how I collect user input for (secondnum)

var secondnum = prompt ("enter b");
while (isNaN(secondnum) || secondnum == "") {
    var secondnum = prompt ("enter a different  b");
}

Thank you in advance.

i don't see where you are calling your discriminant function — Jacob, May 19 '14 at 23:20
Look at the Javascript console. It should show some error. Also, console.log is usually more informative then alert for debugging. — Thilo, May 19 '14 at 23:21
@Atutouato Its recommended, but its not strictly necessary in this case since both `isNaN` and `Math.pow` accept stringtegers. — aebabis, May 19 '14 at 23:23
@acbabis, ah, I see. I never knew that before... I guess you learn something every day here. — Atutouato, May 19 '14 at 23:24

score 0 · Accepted Answer · answered May 19 '14 at 23:30

I am not 100% sure on the math, but syntactically I think you are trying to do something like this

function discriminant(secondnum,firstnum,thirdnum) {
     var disc = Math.sqrt(Math.pow(secondnum,2)-(4*firstnum*thirdnum));
     return disc;
}

ans1 = ((-1*secondnum) + discriminant(firstnum, secondnum, thirdnum))/(2*firstnum);
ans2 = ((-1*secondnum) - discriminant(firstnum, secondnum, thirdnum))/(2*firstnum);

window.alert(ans1);
window.alert(ans2);

which will at least get your alert boxes working provided firstnum, secondnum and thirdnum are declared before this block executes

JavaScript window.alert not working

1 Answers1