JavaScript Prompt Validation for Integer Input - javascript

I found myself needing to create a function to validate the input of a JS prompt as an integer. It turns out there is a little subtlety involved as pressing cancel returns null.
What I originally tried (ported from a Python program) was:
function getInteger() {
let number = null
while ( number == null ) {
let value = prompt( "Guess number: " )
if ( isNaN( value ) ) {
alert( "Invalid input." )
} else {
number = parseInt( value )
}
}
return number;
}
However, this returns NaN if I cancel the prompt, which doesn't make sense as a return value (it seems isNaN(null)returns false). (By doesn't make sense, I mean "can't be meaningfully used by the rest of the program as it's not descriptive of what happened").
So after some thought, I came up with:
function getInteger(){
while(true){
let input = prompt("Input number: ");
if (input && isNaN( input ) ) {
// user pressed OK, but input invalid
alert("Invalid input.");
} else if (input) {
// user typed something valid and hit OK
return parseInt(input);
} else {
// User pressed cancel
alert("I'm out of here.")
return;
}
}
}
getInteger()
I'm curious as to whether I've covered all possible inputs? Also, whether my code is "well written" - is there a better way to do it? Is using while(true) considered a bad idea?
I'm aware that prompts in general are probably a bad idea, but that's not the point here.
Any help appreciated.

I run your code above, i try to input nothing and press OK and its show alert like i cancel the prompt. I think you should check also whether user input something or nothing. Your code might be looks like this:
function getInteger(){
while(true){
let input = prompt("Input number: ");
if (input == null) {
// user hit cancel
alert("I'm out of here.")
return true;
} else{
if (input.length<=0 || isNaN( input ) ) {
// user pressed OK, but input invalid or does not input anything
alert("Invalid input.");
} else {
// user typed something valid and hit OK
return parseInt(input);
}
}
}
}
getInteger()

Can't answer about this prompt function behavior, but your last code is equivalent to:
let input;
while (input = prompt("Input number: ")) {
if (isNaN(input)) {
alert("Invalid input.");
} else {
return parseInt(input);
}
}
Still outside the prompt behavior stuff, if you expect an integer (i.e. only figures) in your input string, I would tend to test this with a regular expression like /^\d+$/, instead of isNaN (what if I input "1.25"? Result wouldn't be NaN, and it'd return 1, but it doesn't seem to be what you intend to achieve).
EDIT the code is not exactly equivalent, so let's make it so:
let input;
while (input = prompt("Input number: ")) {
if (isNaN(input)) {
alert("Invalid input.");
} else {
return parseInt(input);
}
}
alert("I'm out of here.");
return;

Related

How to give "No more tries left" in a password-guessing loop

I've just started learning JS and I got stuck here.
What I need to do:
If you don't enter the correct password, you get the message "Try again".
If you don't enter the password 3 times, you get the message "No more tries left".
If you enter the correct password, you get the message "You may enter".
Here's my code:
for ( let i = 3; i > 0; i-- ) {
let password = prompt("What is the password?")
if ( password.toUpperCase() !== "BINGO" ) {
alert("Try again")
} else if ( i = 0 ) {
alert("No more tries left")
} else {
alert("You may enter")
}
}
I can't get it work properly as the message "No more tries left" doesn't show up. I know ( i = 0 ) is wrong but I don't know how to make it work.
Firstly, make sure that you're not using an assignment operator when you check if i == 0. You're currently using i = 0, which doesn't check if the two are equal as much as it assigns the left to the right. No bueno.
Secondly, your for loop is off just by a bit. It'll never get to 0 because you've asked it to loop while i > 0, not i >= 0. But wait - if you use i >= 0, it'll loop four times. That's not what you want either. We'll compromise and loop three times, but check if i == 1 instead of 0.
Here's my corrected code that works:
// loop three times
for ( let i = 3; i > 0; i-- ) {
let password = prompt("What is the password?")
// if it's the correct answer then alert and break the loop
if ( password.toUpperCase() == "BINGO" ) {
alert("You may enter")
break
// if it's not, and the tries has elapsed, then alert and break the loop
} else if ( i == 1 ) {
alert("No more tries left")
break
// if it's not but the tries have not elapsed, then loop again
} else {
alert("Try again")
}
}
Try this.
for ( let i = 3; i >= 0; i-- ) {
if (i===0){
alert("No more tries left");
break;
}
let password = prompt("What is the password?")
if ( password.toUpperCase() !== "BINGO" ) {
alert("Try again")
} else {
alert("You may enter")
}
}
Give the user chance to enter the password 3 times but loop 4 times and check if the loop runs for 4th times(i === 0). if prompt No more tries left and break the loop.
You are using an assignment operator instead of a comparison operator.
Change this:
else if ( i = 0 ) {
alert("No more tries left")
}
To this :
else if ( i == 0 ) {
alert("No more tries left")
}
Try this. It will run the loop until they have entered the password correctly or the number of attempts is 3.
After the loop you can then just check if valid is true or false.
let valid = false;
let attempts = 0;
do
{
const password = prompt('What is the password');
valid = password.toUpperCase() === 'BINGO';
if (!valid && attempts < 2)
{
alert('Try again');
}
attempts++;
} while (!valid && attempts < 3)
if (valid)
{
alert('You may enter');
} else
{
alert('No more tries left');
}
You are asking the user to enter the password in each iteration
using a loop. So, showing that "you don't have anymore attempt left"
is useless here. Because if the value is greater than 3, the
instruction inside the loop will not be executed.
Do not use JavaScript for authentication. It is a client side
programming language and any one who knows how things work can
extract the password. Instead use a back-end language for
authentication such as PHP, Node.js
But if you only want to know about it just for the learning purpose
not because you wanna implement it, the below code will help you
for (let i=0; i<3; i++){
let password = prompt("what is the password: ");
if (password.toUpperCase() != "BINGO"){
alert("Try Again!");
}else{
alert("You may enter!");
i=3;
}
}
There are several ways you can do the "No more attempt left" is, one of the simple and basic is:
<input type="button" value="Enter Code" onclick="checkMe()">
<script>
let i=0;
function checkMe(){
if (i<3){
let password = prompt("Enter password!");
if (password.toUpperCase() != "BINGO"){
alert("Try Again! Attempt "+ (++i));
}else{
alert("You may enter!");
i=3;
}
}else alert("No more attempts left");
}
</script>
The above code can be implemented using input field, as i said, there are several ways. Hope it helps!
Your code is fine, what goes wrong is that it does not fall into the if condition (i == 0), because the loop only runs while i > 0,
just need to adjust like this:
for ( let i = 3; i > 0; i-- ) {
let password = prompt("What is the password?")
if (password.toUpperCase() !== "BINGO" && i > 1 ) {
alert("Try again")
} else if (i == 1 && password.toUpperCase() !== "BINGO") {
alert("No more tries left")
} else {
alert("You may enter")
i = 0
}
}

A banking function that loops user input and increments/decrements until exit key is entered in js

I am trying to write a function that gives a user 4 choices, does what they choose and then asks them the first 4 choices again and again until they exit.
I have tried using an if/else loop inside a while loop, but that just takes the first user input and loops at that point. It also concatenates the balance when I try to add the two numbers. I assume that due to the fact that the prompt is a string and assigns a string to the variable. I am using console.log() to try and see what is happening while everything is running, but to no avail.
Sorry if this is a lengthy post and redundant.
let balance = 0;
let deposit = 0;
let withdraw = 0;
function bankFunction (banked) {
alert('Hello, how can I help you today?');
let input = prompt('Q to quit the application \nW to withdraw \nD to deposit \nB to view balance');
while (input != 'Q') {
if (input === 'W') {
withdraw = prompt("Withdraw how much?");
console.log(withdraw);
balance = balance - withdraw;
console.log(balance);
} else if (input === 'D') {
deposit = prompt("Deposit how much?");
console.log(deposit);
balance = balance + withdraw;
console.log(balance);
} else {
alert("done");
break;
}
}
}
If you want to continuously prompt the user for inputs, then the prompt function should be inside your loop too. The essential pseudo code is: "While the input is not "Q", continue to prompt for a user choice".
Implementation:
let input = "A" // Initial input to get the loop working
while (input !== "Q") {
// Get actual user input
input = prompt("Choose Q or W or D or B");
if (input === "W") {
// Withdraw logic
}
else if (input === "D") {
// Deposit logic
} else if (input === "B") {
// ...
}
}
Note that there is a bit of a little gimmick here: I needed to have an initial input ("A") to get the first round of the loop working - since in the first round of the loop, user input has not been received yet. Once it get past that initial first round, the input variable is being continuously re-assigned through the user prompt, and the loop will exactly how the pseudo-code described it.
If you don't like that gimmick, there is another way, called the While-True-Break loop. The essential idea is that: The loop will automatically run forever, until you explicitly stop it (via break statement)
let input;
while (true) {
input = prompt("Choose Q or W or B or D");
if (input === "Q") {
// Stop the program loop
break;
} else if (input === "W") {
// ...
} else if ...
}

Typeof in IF works but ELSE of same statement fails

I'm attempting to create a javascript variable str. The ID idofnet may not exist, if it doesn't I want to ask for a value for str. If it does exist I want to pick it up from the ID. Here is my code...
function ics214button() {
if (typeof $("idofnet").html() === "undefined") {
var str = prompt("Enter a Log number.");
} else {
var str = $("#idofnet").html().trim();
}
if (str =="") {alert("Sorry no net was selected");}
else {alert ("It worked");}
}
When I test this knowing there is no ID = idofnet, I get the prompt to enter a log number. And the rest of the code executes properly.
But when the idofnet does exist and it contains a value, I still get the prompt asking enter a log number. The value is never set in the else condition testing for undefined.
If idofnet contains a value, why is it still asking me as if it were undefined? The var str will always be a number.
Changing the if condition test to this:
if ( $('#idofnet').length ) {
var str = $("#idofnet").html().trim();
} else {
var str = prompt("Enter a Log number.");
}
Solved the problem.

Check if key is in array-JavaScript

I have this JavaScript code
function checkTextField() {
var textVal = document.getElementById("textfield").value;
if (textVal == '', textfield.value.length <= 31)
{
alert('Wrong Key-Code. Key-Code must have 32 characters!');
}
else //Its all about how to decrypt a database file called ,,Salam Horia Allah,,!(good luck hackers)
{
{
var text = document.getElementById("textfield").value;
if (text ==
"3e6898f92134d05408dfed30b268d9d6",
"fa0f82cc02a6cdc35072ee5ce2b0c379",
"6a1df566fcaabca717aa1b81c3e0bd31",
"dc0beea186c5f5c2110bedbeccc5a7aa",
"1a317dbc4587268809b67179c391a5da9debb6261e3a3bcf7e6cd2b34356fc40",
"08a8c9750b3d184e6450b98fa90208bbd6c07171c0cce929bc52be1fdb44b09c",
"ac8ce3072f41269be4626539650bb1981c2939db0ffd576f240d06b0b7470c11",
"23a306626c5e9f83d8ce6012f9209fb8f3adcc1a098ffbfafd3c7965ed2c30a6",
"teBy%udu#uMuGyZe4uTyHeNa5yLy6avyTumypy8uHaGujytaWy",
"SezyDuXaquneguzuLatydy7e2ygu4y5e7uqe3e6uheVuVeSumu"
)
{
location.href = "http://79.115.70.31:8521/InWork/"
}
else {
alert("Wrong Key")
}
}
}
}
and here is what happen:
i have a textbox and a button,when i insert a key from if (text ==
"3e6898f92134d05408dfed30b268d9d6",
"fa0f82cc02a6cdc35072ee5ce2b0c379",
"6a1df566fcaabca717aa1b81c3e0bd31",
"dc0beea186c5f5c2110bedbeccc5a7aa",
And when someone press that button, I want that script to check if one of that keys are in text field, if is true the request will send to another page, if is not true, show an alert.
But my problem is, whatever I write in that textbox it send me to that page, also I got an alert if textbox have <31 characters.
The comma operator works inside of an if clause, but it takes the last value, not a logical OR, which is here required.
(An input returns always a string and if empty, the string length is zero. A check for emptiness and a check for a length which is smaller than a value is superfluous, because the length check includes a zero length as well.)
if (textVal == '' || textfield.value.length <= 31)
// ^^
Beside that, I suggest to use an array for the valid keys for checking and check only if the value is in the array, then proceed or give an alert.
Another point is to assign the value of the input only once and use it in the whole function with the variable. Do not use a mixed style with a variable and document.getElementById("textfield").value together.
function checkTextField() {
var keys = ["3e6898f92134d05408dfed30b268d9d6", "fa0f82cc02a6cdc35072ee5ce2b0c379", "6a1df566fcaabca717aa1b81c3e0bd31", "dc0beea186c5f5c2110bedbeccc5a7aa", "1a317dbc4587268809b67179c391a5da9debb6261e3a3bcf7e6cd2b34356fc40", "08a8c9750b3d184e6450b98fa90208bbd6c07171c0cce929bc52be1fdb44b09c", "ac8ce3072f41269be4626539650bb1981c2939db0ffd576f240d06b0b7470c11", "23a306626c5e9f83d8ce6012f9209fb8f3adcc1a098ffbfafd3c7965ed2c30a6", "teBy%udu#uMuGyZe4uTyHeNa5yLy6avyTumypy8uHaGujytaWy", "SezyDuXaquneguzuLatydy7e2ygu4y5e7uqe3e6uheVuVeSumu"],
text = document.getElementById("textfield").value;
if (keys.indexOf(text) !== -1) {
location.href = "http://79.115.70.31:8521/InWork/";
} else {
alert("Wrong Key");
}
}
Well you need to compare you tex with each key available so
function checkTextField() {
var textVal = document.getElementById("textfield").value;
var yourKeys =[ "3e6898f92134d05408dfed30b268d9d6",
"fa0f82cc02a6cdc35072ee5ce2b0c379",
"6a1df566fcaabca717aa1b81c3e0bd31",
"dc0beea186c5f5c2110bedbeccc5a7aa",
"1a317dbc4587268809b67179c391a5da9debb6261e3a3bcf7e6cd2b34356fc40",
"08a8c9750b3d184e6450b98fa90208bbd6c07171c0cce929bc52be1fdb44b09c",
"ac8ce3072f41269be4626539650bb1981c2939db0ffd576f240d06b0b7470c11",
"23a306626c5e9f83d8ce6012f9209fb8f3adcc1a098ffbfafd3c7965ed2c30a6",
"teBy%udu#uMuGyZe4uTyHeNa5yLy6avyTumypy8uHaGujytaWy",
"SezyDuXaquneguzuLatydy7e2ygu4y5e7uqe3e6uheVuVeSumu"];
if (textVal == '', textfield.value.length <= 31)
alert('Wrong Key-Code. Key-Code must have 32 characters!');
else {
var text = document.getElementById("textfield").value;
var i = yourKeys.length;
while(i--){
if(text == yourKeys[i] )
location.href = "http://79.115.70.31:8521/InWork/"
else
alert("Wrong Key")
}
}
}

Using JS to check if integer is even or pressing q to quit

The objective here is for the user to enter a number to determine whether it is even or to enter 'q' to quit the program.
var readlineSync = require('readline-sync');
var i = 0;
while (i <= 3) {
var num = readlineSync.question("Enter q to quit, or enter an integer to continue?");
if (num === 'q') {
console.log("You have quit the application. Thanks for using.");
break;
}
else if (num % 2) {
console.log("You have entered an odd number");
}
else if (num !== 'q') {
console.log("You have not entered a valid character. Please try again.");
break;
}
else {
console.log("You have entered an even number.");
break;
}
}
Pressing q initiates the appropriate response and exits the program. Entering an odd number also generates the appropriate response. However if an even number is entered, the program does not generate the appropriate response and instead reads You have not entered a valid character. Please try again. What am I overlooking? Any advice is appreciated.
It's because of your third condition (num !== 'q'). It evaluates as true when you enter an even number.

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