Develop Reference

Find the output using typeof function

I am writing a code. And here I have a problem how can I fix that. I have an input line, it takes a string or a number. So I need to check what is the output and get the answer. I need to give a simple solution. So I can't use functions or something like that.
let input = prompt('Enter your text.');
if (typeof input === "string") {
alert("You have string.");
} else if (typeof input === "number" && input > 30) {
alert("number more than 30");
} else if (typeof input === "number" && input < 30) {
alert("number less then 30");
}

prompt will always return a string.
If you want to check whether the string is composed purely of numerical values, you could use a regular expression:
if (/^[+-]?\d+(?:\.\d+)?$/.test(input)) {
// then it's purely numerical
const num = Number(input.trim());
// perform more operations on the number
} else {
// it's not composed of only numerical characters
}
If you don't want to use a regex, you can use Number alone, but then you'll also include values like Infinity which might not be desirable, and since Number('') gives 0, you'll have to check for that separately:
const num = Number(input);
if (input.trim().length && !Number.isNaN(num)) {
// then it's a number, use num
}
Another approach that I'd recommend is to avoid prompt entirely. Consider using a proper modal instead, such as a form with an input box and a submit button.
In such a case, if you want to require a numeric input, just do:
<input type="number">

I had a similar problem a few weeks ago and this is what I did:
function testNumber(test) {
if (isNaN(test) === false) {
console.log("this is a number");
} else {
console.log("this is not a number");
}
}
testNumber(4); // number
testNumber("4") // number
testNumber("string") // not a number
You can replace "test" for a variable if you don't want to use a function
if (isNaN(myVar) === false) {}
And you may want to add more checks if you want to differentiate between 4 and "4"

You can do
let input = prompt('Enter your text.');
if(isNaN(Number(input))){alert("You have string.")};
if (Number(input) > 30) {
alert("number more than 30");
} else if (Number(input) < 30) {
alert("number less then 30");
}
So it can change all Stringed-numbers to numbers and check if they are number with the isNaN function

Do while loop until user enters valid input

I need to create a do while loop that accepts any user input until a number is entered. my loop doesn't execute as expected. please help.
can i do without the maximum and the minimum values?
var number;
var minimum = 1;
var maximum = 20
window.prompt("Please enter a number between 1 and 20");
do {
if (number >= minimum && number <= maximum)
break;
else(window.prompt("Invalid input, please enter a number between
1 and 20 "));
}
while (number < minimum || number > maximum);

The code below works for you.
It's basically the same as yours, but I made it much more efficient and readable.
A few things I changed for you was:
window.prompt and prompt do the same thing. In other words, the window is unnecessary typing, so use just prompt.
prompt alone just asks for an input. It doesn't store it anywhere, or do anything with it. For you to be able to do anything with it, you need to set the value of a variable to equal it. I set number to equal the prompt
You can use isNan() to check if it is a string or a number.
var number = prompt("Please enter a number between 1 and 20");
var minimum = 1;
var maximum = 20
do {
if (isNaN(number)) {
break;
}
else {
number = prompt("Please enter a valid number between 1 and 20");
}
}
while (!isNaN(number));

Javascript user input validation

My exercise is to force a user to type a number and check that it is less than 100. I think I've done this well but there is another case I don't know how to do. If the user does not type any number in the space, the program should show something like "you must type a number". How should I write the code?
var number=prompt('enter a number');
if (number<100){
newnumber=100-number;
document.write(number+'is less than 100 by'+ newnumber);
}else if(number>100){
document.write('type again');
}

You can determine if the users input is a valid number by using the isNaN function. I have also validated the blank character for you, as shown below.
var isValid = !isNaN(number) && number !== "";
Full snippet:
var number = prompt('enter a number');
number = number.replace(/\s/g, "");
var isValid = !isNaN(number) && number !== "";
if (isValid) {
if (number<100) {
newnumber=100-number;
document.write(number+'is less than 100 by'+ newnumber);
} else if(number>100) {
document.write('type again');
}
} else {
document.write("Looks like you didn't enter a valid number");
}
https://jsfiddle.net/ezgn5cv5/

var number = null;
while (number !== 0 && !number || number >= 100) {
number = parseInt(prompt('Enter a number, less than 100'));
}
document.write(
number +
' is less than 100 by ' +
(100 - number)
);
This puts us in a loop for whether or not the number is a valid integer (I assumed that's what you wanted, but you could change this to float or something else), and under 100. Only when the user's input is valid will it go to the line to output.
The second condition for the while loop is !number. This basically tests for falsy conditions, such as NaN or null. If parseInt() can't figure out what the user typed in for a number, it will return NaN. And, of course, we initialized the number variable to null.
The first condition for while is number !== 0 is actually required because of the second condition which tests for falsy. 0 is falsy, but 0 is a valid number less than 100, so we need to make sure that we let 0 be valid. Conditionals like these short circuit. That means that they are processed from left to right, and any condition failing the test will immediately bypass the conditional block of code below. If number is 0, we know that the whole condition is false and we can move on.
The third condition simply ensures we're under 100 by re-prompting if we're not.
Also, I should note that document.write() has some issues. It's better to select an element on the page and set its text.

Remove all spaces .replace(/\s/g, "").
Detect if user input a number using parseFloat() if you want to allow
user to input decimal numbers like 5.254 or only integers using
parseInt() like 5.
Then detect if number > 100 or number < 100.
See this example:
var number = prompt('enter a number');
number = number.replace(/\s/g, ""); //remove all spaces
if (number != "") { // if not empty
if (parseFloat(number) == number) { // if decimal/integer number
if (number < 100) {
newnumber = 100 - number;
document.write(number + ' is less than 100 by ' + newnumber);
} else if (number > 100) {
//number = prompt('enter a number');
document.write('type again');
}
} else {
//number = prompt('enter a number');
document.write('you must type a number');
}
} else { // if empty input
//number = prompt('enter a number');
document.write('shouldn\'t be empty');
}

Why is my code not able to recognize that a password contains characters?

I am making a login form. Before it submits, I check if all the fields are filled in. I also check if the password is longer than 7 characters and contains at least one number, at least one character, and no spaces. My current code keeps on telling me that I am missing a character no matter what I enter. This is the code:
if($("#password").val()==""){
error += "The password is required.<br>";
}
else if($("#password").val().length<8){
error += "Your password needs at least 8 characters.<br>";
}
else if($("#password").val().length >= 8){
var pass = $("#password").val().split("");
var hasNum = false;
var hasChar = false;
var hasSpace = false;
for(var i = 0; i < pass.length; i++){
if(pass[i] == " "){
hasSpace = true;
}
else if(Number(pass[i]) == NaN){
hasChar = true;
}
else if(Number(pass[i]) != NaN){
hasNum = true;
}
}
if(!hasChar){
error += "Your password must contain at least one character.<br>";
}
if(!hasNum){
error += "Your password must contain at least one number.<br>";
}
if(hasSpace){
error += "Spaces are not allowed in a password.<br>";
}
}
I first check for a space. Then I check if a character can be converted to a number. If not, then it must be a string. If it can be converted, it must be a number. Whatever I type in, it always says "Your password must contain at least one character". How can I fix this? I will give you more code if it is necessary.

The problem is that NaN compares unequal (via ==, !=, ===, and !==) to any other value, including to another NaN value:
NaN === NaN;// false
Number('S') == NaN; //false
Number(10) == NaN; //false
try to use isNaN() instead.

Why is everything NOT prime?

I'm trying to write this program to find prime numbers. I have the basics of it down, except that no matter what number I put in, it returns as NOT prime. I've been messing with this for way too long and cannot figure out what it is. Is it in my "if" statement or my isPrime function? Please help, and thank you!
var number = 0;
function main()
{
number = parseInt(prompt("Please Enter a Number to Determine Whether or Not it is Prime:", "Enter a Number"));
while(isNaN(number) === true)
{ alert("You Entered an Invalid Number. Please Reenter");
number = parseInt(prompt("Please Enter a Number to Determine Whether or Not it is Prime:", "Enter a Number"));
}
isPrime(number);
if(prime = false)
{ alert("The number " + number + " is a Prime Number!"); }
else
{ alert("The number " + number + " is NOT a Prime Number!"); }
}
/*------------------------------------------------------*/
function isPrime(number)
{
if(number < 2)
{return false;}
var prime = false;
for(var i = 2; i <= Math.sqrt(number); i++)
{ if(number % i == 0)
{prime = true;}
}
return prime;
}

if (prime = false)
You just assigned prime to false.
You don't want to do that.
By contrast, you do want to assign it to the result of your function.

Replace:
if(prime = false)
not only because you're using assignment instead of comparison, but because prime is not defined (it's not going to return/create a global variable prime from that function call).
Replace it with:
if (!isPrime(number)) {
Now this doesn't use a variable to store the result of the isPrime call, but uses the call directly. If you need this result in more than one place, then it would be a good idea to assign it to a variable:
var prime = isPrime(number);
and then do the rest of your code:
if (prime == false)...

isPrime(number);
leaves no variable assigned. Therefore prime is never assigned in your test and unassigned variables are treated as false as far as boolean expressions are concerned.
It should be
var prime = isPrime(number);
You're also doing an assignment where you meant to do a comparison.
if(prime = false)
should be
if(prime === false)
Tip: If you're doing these kinds of tests, it's usually a good idea to put the thing that can't be changed by assignment on the left (function call, constant, etc). That way if you accidentally put = instead of == or === the script will fail with an error.
if(false === prime)
If you accidentally type
if (false = prime)
you'll get
ReferenceError: invalid assignment left-hand side
which is obvious and easy to debug.
As this is a simple boolean switch, a simple "is not true" check is fine.
if (!prime)

Actually their are only 2 small logic failure.
You define "prime" inside your function isPrime() - hence you cannot use it outside your function.
You try to do if(prime = false) which assigns the value false to "prime" whick does nothing for your if except breaking it.
You need to define the variable outside hence use your prime = isPrime()
Also you do not need to check against "false" which by any means does not really make sense their. "true == false" ? just skip that ans ask for if(prime) which is true or false.
Alternativly you can call your funtion directily in the if condition like:
if(isPrime(number)){....
it then automaticly checks the return value.