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JavaScript The Solution

NICOLE REBENTISCH
NICOLE REBENTISCH
3,612 Points

I prefer the alert to pop up as soon as a non-number is typed. Is there a more concise way than how I coded it?

The example given by Dave McFarland in the Practice If and Else exercise doesn't pop up an alert until after both values are entered, but I prefer the alert to pop up as soon as a non-number is typed (or if "cancel" is clicked). I came up with the code below to address that, but is there a shorter way to achieve the same result?

// declare program variables
let num1;
let num2 = null;
let failMessage = 0;
let message;

// announce the program
alert("Let's do some math!");

// collect numeric input
num1 = prompt("Please type a number");
num1 = parseFloat(num1);

if (isNaN(num1)){
  alert( "The value you typed is not a number. Reload and try again.");
  failMessage = 1;
}

else if (num1 !== NaN) {

num2 = prompt("Please type another number");
num2 = parseFloat(num2);
}

if (num2 === 0){
  alert("The second number is 0. You can't divide by zero. Reload and try again.");
  failMessage = 1;
}

else if ( (isNaN(num2)) && (num1 !== NaN)){
  alert( "The value you typed is not a number. Reload and try again.");
  failMessage = 1;
}


// build an HTML message
message = `<h1>Math with the numbers ${num1} and ${num2}</h1>
           ${num1} + ${num2} = ${num1 + num2}
           <br>
           ${num1} * ${num2} = ${num1 * num2}
           <br>
           ${num1} / ${num2} = ${num1 / num2}
           <br>
           ${num1} - ${num2} = ${num1 - num2}`;


// write message to web page
 if (failMessage === 0){ 
  document.write(message);
 }

2 Answers

Jonathan Grieve
MOD
Jonathan Grieve
Treehouse Moderator 90,824 Points

Try calling parseFloat() at the end of your prompt, so you don't have the pass the variables into it and call them so many times.

   num1 = prompt("Please type a number").parseFloat();
NICOLE REBENTISCH
NICOLE REBENTISCH
3,612 Points

Adding .parseFloat() to the end of the line throws an error message. Thanks for the idea, though!

Forrest Pollard
Forrest Pollard
1,988 Points

this should work

num1 = prompt("Please type a number");
num1 = parseFloat(num1);
Martín Giavarini
Martín Giavarini
4,036 Points

This should avoid most cases of user input error:

do {
    var num1 = prompt("Please type a number");
    if (isNaN(num1)) {
        alert("The value you typed is not a number. Try again.");
    }
} while (isNaN(num1));

do {
    var num2 = prompt("Please type another number");
    if (+num2 === 0) {
        alert("The second number is 0. You can't divide by zero. Try again.");
    } else if (isNaN(num2)) {
        alert("The value you typed is not a number. Try again.");
    } else {
        result = true;
    }
} while (+num2 === 0 || isNaN(num2));