Develop Reference

javascript if number is evenly divisible true if not false

I have to write Java script that can read two integers from the user, if the first number the user entered is evenly divisible by the second number, then it will display an alert of TRUE to the user, and FALSE otherwise. If either number the user enters is ZERO the alert should display FALSE to the user.
this is my code it does not work
var y = prompt("Enter a Value","");
var z = prompt("Enter a Value","");
if (y % z === 0) {
greeting = "TRUE";
} else (y % z !== 0 ||
{
greeting = "FALSE"
document. get Element By Id ("true false").inner HTML = greeting;

If either number the user enters is ZERO the alert should display
FALSE to the user.
change you if condition to
if (x && y && y % z === 0) {
Rest of the code is
if (x && y && y % z === 0)
{
greeting = "TRUE";
}
else
{
greeting = "FALSE";
}

If you are new to javascript here is another way to implement this very common pattern using the ternary operator:
var greeting = (x && y && y % z === 0) ? "TRUE" : "FALSE";

JavaScript, how to validate if string?

I'm working on a form where my user enters a number between 0-100.
If my user puts in 101, it will return with an alert saying that the numbers are invalid. But how do I validate so he doesn't put in something like "asdfasdf" or if it's just empty?
This is my Validate Script:
function validate() {
var pct = $('#pct').val();
if (pct !== "" && (pct > 100 || pct < 0))
return false;
else
return true;
}

Try this:
function validate() {
var pct = parseInt($('#pct').val());
return (pct <= 100) && (pct >= 0);
}
parseInt('not a number') -> NaN
Comparison result with NaN is always false. So try represent expression as positive and play with it.

How to get alerts for inputed name length of characters - javascript

Hello im trying to do a simple script here when i enter name in input field, i want to get certain alerts for example:
- if name is > 20 characters alert = "name is bigger than 20"
- if name is between 12 and 20 alert = exact number of chars of the name that was inputed
- if name is bigger than 2 chars and bigger or equal than 20 = alert that name
this was just an example of what im trying to do, but im just noob at this point im only 1 month into javascript(html and css) so if anyone can point me in the right direction i would appreciate.
Ok, so far i have this:
<form name="myForm" id="form2" onsubmit="return validate()">
Input name: <input type="text" name = "myName" id="t" />
<input type="submit" name="submit" value="submit" />
</form>
function validate() {
if(document.myForm.myName.value.length>20){
alert("your name is too big");
submitFlag=false; // im not sure what this line does //
} else if(document.myForm.myName.value.length=12-20){
alert("your name is" + document.myForm.myName.value.length + " chars");
} else if(document.myForm.myName.value.length=0){
alert("input name")
}else{
alert("ok e")
}
return submitFlag;
}
THe if statements are workin only if i have two, im getting only the first 2 alerts, so i would like to input more else if statements and to get alerts for them also, i tried to put some more myself, but the dont work, im only getting the first two.

Extending what #dfsq have said,.. you try to get:
if name is between 12 and 20
that means smth like:
document.myForm.myName.value.length > 12 && document.myForm.myName.value.length <= 20
And make your code more simple and readable. And don't forget to return false (your submitFlag):
function validate() {
var len = document.myForm.myName.value.length;
if (len > 20)
{
alert("your name is too big");
}
else if (len > 12 && len <= 20)
{
alert("your name is" + len + " chars");
}
else if (len == 0)
{
alert("input name");
}
else
{
//in fact it would alert when name between 0 and 12
alert("ok e");
}
return false;
}

There are a difference between operators. = is an assignment, == and === are comparison operators. You need latter:
document.myForm.myName.value.length == 0

Here we go:
function validate() {
var charLength = document.myForm.myName.value.length,
submitFlag = false; // This flag would be used further to stop the use going ahead from this particular validation
if (charLength > 20) {
// length more than 20
alert("your name is too big");
} else if (charLength <= 20 && charLength > 12) {
// length between 20 and 12
alert("your name is" + charLength + " chars");
} else if (charLength == 0) {
// If no input there
alert("enter name");
} else {
// Otherwise in success condition
alert("ok e");
submitFlag = true;
}
return submitFlag;
}
Jsfiddle: http://jsfiddle.net/fcwbkkd7/

Javascript - Find if number is positive or negative

I see other solutions to my question but none that help me.
I want to create a function to find if a number is positive/negative. The function should take an integer argument and return true if the integer is positive and false if it is negative.
Also, prompt the user again and again if anything other than a number is entered
Here's the code so far
When I enter a number, it keeps alerting me it is true or false but won't let me enter another.
How do I control my loop so I can ask until -1 is entered? It is not giving me a chance to enter -1
function isPositive(num) {
var result;
if (num >= 0) {
result = true;
} else if (num < 0) {
result = false;
}
return result;
}
var num;
num = parseInt(prompt("Enter a number"));
while (num != -1) {
alert(isPositive(num));
if (isNaN(num)) {
alert("No number entered. Try again");
num = parseInt(prompt("Enter a number"));
isPositive(num);
while (num != -1) {
alert(isPositive(num));
}
}
}

There's a few things wrong with your code, so here's a rewrite with comments:
function isPositive(num) {
// if something is true return true; else return false is redundant.
return num >= 0;
}
// when you want to keep doing something until a condition is met,
// particularly with user input, consider a while(true) loop:
var num;
while (true) {
num = prompt("Enter a number");
// check for null here
if (num === null) {
alert("No number entered. Try again.");
continue; // return to the start of the loop
}
num = parseInt(num, 10); // second argument is NOT optional
if (isNaN(num)) {
alert("Invalid number entered. Try again.");
continue;
}
// once we have a valid result...
break;
}
// the loop will continue forever until the `break` is reached. Once here...
alert(isPositive(num));

Math.sign(number)
which returns either a 1, -1 or 0
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/sign

The number 0 is neither positive, nor negative! :P
function isPositive(num)
{
if(num < 0)
return false;
else
return true;
}
Or a simple way,
function isPositive(num)
{
return (num > 0);
}

You are testing if it isn't -1. Try this:
if(num < 0){
...IS NEGATIVE...
}else{
...IS POSITIVE...
}
This checks if it is less than or greater than 0.

Multiple Logical Operators in javascript

I want to check the following
1: Is x a number
2. If x is less that 5 or greater than 15, sound alert
3. If all is ok, callMe()
var x = 10;
if (isNaN(x) && ((x < 5) || (x > 15))) {
alert('not allowed')
}
else
{
callMe();
}
What am I doing wrong?

var x = 10;
if (isNaN(x) || (x < 5) || (x > 15)) {
alert('not allowed')
}
else
{
callMe();
}
This way, if x is not a number you go directly to the alert. If it is a number, you go to the next check (is x < 5), and so on.

All the other answers about the && vs || are correct, I just wanted to add another thing:
The isNaN() function only checks whether the parameter is the constant NaN or not. It doesn't check whether the parameter is actually number or not. So:
isNaN(10) == false
isNaN('stackoverflow') == false
isNaN([1,2,3]) == false
isNaN({ 'prop' : 'value'}) == false
isNaN(NaN) == true
In other words, you cannot use it to check whether a given variable contains a number or not. To do that I'd suggest first running the variable through parseInt() or parseFloat() depending on what values you expect there. After that check for isNaN(), because these functions return only numbers or NaN. Also this will make sure that if you have a numeric string then it is also treated like a number.

var x = 10;
if (isNaN(x) || (x < 5) || (x > 15)) {
alert('not allowed')
}
else
{
callMe();
}