Develop Reference

Cannot determine if user input is blank javascript

I am creating a voting system webpage using Javascript. There are several things the user must input before beginning the vote, such as candidates, number of people voting, etc. I have created a function for each one, but when I attempted to add some validating if statements to my enterCandidate function, it would not register an error when the user left the box blank. Here is the function code:
var enterCandidate = prompt("Please enter a candidate");
for (let i = 0; i < enterCandidate.length; i++){
if (isNaN(enterCandidate.charAt(i)) || enterCandidate.charAt(i) == ' '){
if (!enterCandidate.length == 0){
candidates.push(enterCandidate);
console.log(enterCandidate);
candidate1 = candidates[0];
candidate2 = candidates[1];
candidate3 = candidates[2];
candidate4 = candidates[3];
candidate5 = candidates[4];
candidate6 = candidates[5];
} else {
alert('Please do not leave the box blank.');
}
} else {
alert('Please enter a name, without symbols or numbers.');
}
}
}
The part I am having an issue with is the second if statement, where I used !enterCandidate.length == 0. This should only return true if the user has inputted something but instead it returns false and moves to the else alert 'Please do not leave the box blank'. I am aware that even if this code worked, it would allow people to enter just spaces - I am not really sure how to tackle that without registering errors if people entered full names.

Why this regular expression return false?

i have poor eng, Sorry for that.
i'll do my best for my situation.
i've tried to make SignUpForm using regular expression
The issue is that when i handle if statement using the regular expression
result is true at first, but after that, become false. i guess
below is my code(javascript)
$(document).ready(function () {
var idCheck = /^[a-z]+[a-z0-9]{5,19}$/g; // more than 6 words
var pwCheck = /^(?=.*[A-Za-z])(?=.*\d)[A-Za-z\d]{8,}$/; // more than 8 words including at least one number
var emCheck = /^([\w-]+(?:\.[\w-]+)*)#((?:[\w-]+\.)*\w[\w-]{0,66})\.([a-z]{2,6}(?:\.[a-z]{2})?)$/; // valid email check
var signupConfirm = $('#signupConfirm'),
id = $('#id'),
pw = $('#pw'),
repw = $('#repw'),
email =$('#email');
signupConfirm.click(function () {
if(id.val() === '' || pw.val() === '' || email.val() === ''){
$('#signupForm').html('Fill the all blanks');
return false;
} else {
if (idCheck.test(id.val()) !== true) {
$('#signupForm').html('ID has to be more than 6 words');
id.focus();
return false;
} else if (pwCheck.test(pw.val()) !== true) {
$('#signupForm').html('The passwords has to be more than 8 words including at least one number');
pw.focus();
return false;
} else if (repw !== pw) {
$('#signupForm').html('The passwords are not the same.');
pw.empty();
repw.empty();
pw.focus();
return false;
}
if (emCheck.test(email.val()) !== true) {
$('#signupForm').html('Fill a valid email');
email.focus();
return false;
}
}
})
});
after id fill with 6 words in id input, focus has been moved to the password input because the condition is met.
but after i click register button again, focus move back ID input even though ID input fill with 6 words
i've already change regular expression several times. but still like this.
are there Any tips i can solve this issue?
I hope someone could help me.
Thank you. Have a great day

Do not use the global flag on your regexes. Your code should be:
var idCheck = /^[a-z]+[a-z0-9]{5,19}$/;
When you match with the /g flag, your regex will save the state between calls, hence all subsequent matches will also include the previous inputs.

use
var idCheck = /^[a-z]+[a-z0-9]{5,19}$/
removing the g flag
and modify the line
else if (repw.val() !== pw.val()) {

Javascript Eval() thinks first value is a function

I am writing a function that will evaluate expressions in an input field and return the sum.
Currently is working but I am running into an error that I just cannot figure out. Here is my code in Plunker.
function linkFunction(scope) {
var PO = 10;
scope.value = PO;
scope.result = '';
scope.Evaluate = function (input) {
if (input.match(/[a-zA-Z]/g) != null) { //to check if user has inputted a letter between a-z, case sensitive.
return alert("You must only use numbers, not letters")
} else if (input.match(/[!"^£$&[{}\]?\\##~<>_'|`¬:;,=]/g) != null) { //to check if user has inputted a special symbol
return alert("You must only use the symbols specified")
} else if (input.match(/\.\d*\.+/g) != null) { //to check if user has inputted a doubled decimal eg 10.2.2
return alert("You can only use 1 decimal point")
} else if (input.match(/\.{2,}/g) != null) {//to check if user has inputted a two decimals eg 10..1
return alert("You cannot put two decimals one after another")
}
// if (input.match(/\d*\(\d\W\d\)/g) != null){
// }
var percentPattern = /[0-9]*\.?[0-9]+%/g;
var expressionResults = input.match(percentPattern);
if (scope.enablePercentage) { //if parameter = 1, then do this code.
if (expressionResults != null) { //if user has entered into the input field
if (expressionResults.length > 1) { //if you user has finished the RegEx (%, is the end of the RegEx, so code will think its the end of the array, therefore you cannot add another %)
return alert("Too many % values");
} else {// user has met all requirements
var percentageValue = parseFloat(expressionResults) * PO / 100;
input = input.replace(expressionResults, percentageValue);
}
}
} else if (expressionResults != null) { //if parameter = 0, then do this code. Parameter is off, but user has entered percentage
return alert("You cannot use %");
}
scope.result = eval(input);
}
}});
If you write 10(5+3) it gives you an error
TypeError: 10 is not a function
Obviously if a user ran this code they would expect to see the value 80.
Eval thinks that 10() is a function.
Does anyone know how to fix this problem. Thanks

eval expects you to pass it JavaScript, not algebra.
If you want to multiply two values together then you must use a Multiplicative Operator.
10 * (5+3)

Number validation in JavaScript

I have created an external JavaScript to validate a form I created in HTML. Some of the validation works, but when I use the same code to validate other fields it will not work. E.g. postcode must contain numbers - if not, postcode is invalid.
I tried using the same code for a credit card, i.e. credit card must have 16 digits - if not, the credit card number is invalid. I wrote the code for postcode and it worked, but when I tried to reaarrange it to suit the credit card function, it did not work. Not too sure why? Should I have used a different function?
Here is my external javascript:
function validateForm()
{
if (isNaN(document.getElementById("postcode").value))
{
alert ("Your postcode is not valid");
}
else
{
alert ("You have entered your postcode correctly");
}
if (document.getElementById ("email").value.length < 5 ||
document.getElementById ("email").value.indexOf("#")== -1)
{
alert("Please enter your email min 5 chars and include # symbol");
document.getElementById("email").focus();
return false;
}
if (isNaN(document.getElementById("creditcard").value))
{
alert ("Your creditcard is not valid");
}
else
{
alert ("You have entered your creditcard correctly");
}
alert("Thank you for your submission!");
return true;
}

So first off, you probably don't want to prompt the user with 10 error dialogs at a time.
So you should nest your if else clauses & the function will stop after the first error.
Second, isNaN is doubtfully a good evaluator because input.value may return a value of type string. Using a regex is a more robust way of error checking inputs. Third, you want to account for the user's confusion mistakes. Users often think (me too): 'wait, should I also write the dash on my credit card here?'.
So you'll remove dots, dashes & whitespace before proceeding (those could unknowingly be included). Other chars are just invalid. For your credit card input, that would be:
var ccVal = document.getElementById("creditcard").value;
// remove dots, dashes & whitespace
ccVal = ccVal.replace(/(\s|\.|\-)/g, '');
// if any other chars there, input value = incorrect & stop function
if ( ccVal.match(/\D/) ) {
alert('A credit card number only has decimals, silly.');
return false;
} else {
// Check for length now
if ( ccVal.length !== 16) {
alert('A credit card has 16 decimals, silly.');
return false;
} else {
// more checks
document.getElementById('myform').submit()
}
}
See an implementation example here: http://jsbin.com/betawahi/1/edit

isNaN checks if the value is not an integer, you'll need an additional check for the length.
Keeping the code similar to the way you've set out the rest of the function, to check if the credit card is a number and a length of 16, you'll want:
if( !(isNaN(document.getElementById("creditcard").value) && document.getElementById("creditcard").value.length === 16) {
alert("Credit Card Is Valid");
}else{
alert("Your Credit Card is Not Valid");
return false;
}

how validate an email that allows specific number of dots before and after # symbol

var val_em=document.add_indus_detail_form.txt_email.value;
var atpos=val_em.indexOf("#");
var dotpos=val_em.lastIndexOf(".");
if(val_em!='')
{
if (atpos<1 || dotpos<atpos+2 || dotpos+2>=val_em.length)
{
alert("Not a valid e-mail address");
return false;
}
}
i use this condition to check the email validation that user enters in the textbox how i can validate it like it allows 3 or 4 or any specific numbers of dot allow (ex abc.abc.abc.abc#abc.abc.com) before and after the # but do not allow that dots together (ex: abc#abc...com). also do not allow the spaces in email how it will be have you any idea for this type of validation..

I would suggest a regex for this
function validateEmail(email){
var emailReg = new RegExp(/^(("[\w-\s]+")|([\w-]+(?:\.[\w-]+)*)|("[\w-\s]+")([\w-]+(?:\.[\w-]+)*))(#((?:[\w-]+\.)*\w[\w-]{0,66})\.([a-z]{2,6}(?:\.[a-z]{2})?)$)|(#\[?((25[0-5]\.|2[0-4][0-9]\.|1[0-9]{2}\.|[0-9]{1,2}\.))((25[0-5]|2[0-4][0-9]|1[0-9]{2}|[0-9]{1,2})\.){2}(25[0-5]|2[0-4][0-9]|1[0-9]{2}|[0-9]{1,2})\]?$)/i);
var valid = emailReg.test(email);
if(!valid) {
return false;
} else {
return true;
}
}
call the function validateEmail whenever you need....

Validations in JavaScript are useless. The user can turn off JS or maybe you encounter a browser who cant even understand JS. This makes your page vulnerable to attacks. So NEVER use JS for validating user inputs.
What you want is RegEx or many if-conditions together with string-functions. My approach: Use a For-Loop, go through the string one by one, check the current character and the one after it. Like this:
for($i = 0; $i < strlen($string); $i++) {
if(substr($string, 0, 1) == '.' {
//do something
}
}