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getting wrong answer for finding largest of 2 numbers using readline-sync in js [duplicate]

I store some parameters client-side in HTML and then need to compare them as integers. Unfortunately I have come across a serious bug that I cannot explain. The bug seems to be that my JS reads parameters as strings rather than integers, causing my integer comparisons to fail.
I have generated a small example of the error, which I also can't explain. The following returns 'true' when run:
console.log("2" > "10")

Parse the string into an integer using parseInt:
javascript:alert(parseInt("2", 10)>parseInt("10", 10))

Checking that strings are integers is separate to comparing if one is greater or lesser than another. You should always compare number with number and string with string as the algorithm for dealing with mixed types not easy to remember.
'00100' < '1' // true
as they are both strings so only the first zero of '00100' is compared to '1' and because it's charCode is lower, it evaluates as lower.
However:
'00100' < 1 // false
as the RHS is a number, the LHS is converted to number before the comparision.
A simple integer check is:
function isInt(n) {
return /^[+-]?\d+$/.test(n);
}
It doesn't matter if n is a number or integer, it will be converted to a string before the test.
If you really care about performance, then:
var isInt = (function() {
var re = /^[+-]?\d+$/;
return function(n) {
return re.test(n);
}
}());
Noting that numbers like 1.0 will return false. If you want to count such numbers as integers too, then:
var isInt = (function() {
var re = /^[+-]?\d+$/;
var re2 = /\.0+$/;
return function(n) {
return re.test((''+ n).replace(re2,''));
}
}());
Once that test is passed, converting to number for comparison can use a number of methods. I don't like parseInt() because it will truncate floats to make them look like ints, so all the following will be "equal":
parseInt(2.9) == parseInt('002',10) == parseInt('2wewe')
and so on.
Once numbers are tested as integers, you can use the unary + operator to convert them to numbers in the comparision:
if (isInt(a) && isInt(b)) {
if (+a < +b) {
// a and b are integers and a is less than b
}
}
Other methods are:
Number(a); // liked by some because it's clear what is happening
a * 1 // Not really obvious but it works, I don't like it

Comparing Numbers to String Equivalents Without Using parseInt
console.log(Number('2') > Number('10'));
console.log( ('2'/1) > ('10'/1) );
var item = { id: 998 }, id = '998';
var isEqual = (item.id.toString() === id.toString());
isEqual;

use parseInt and compare like below:
javascript:alert(parseInt("2")>parseInt("10"))

Always remember when we compare two strings.
the comparison happens on chacracter basis.
so '2' > '12' is true because the comparison will happen as
'2' > '1' and in alphabetical way '2' is always greater than '1' as unicode.
SO it will comeout true.
I hope this helps.

You can use Number() function also since it converts the object argument to a number that represents the object's value.
Eg: javascript:alert( Number("2") > Number("10"))

+ operator will coerce the string to a number.
console.log( +"2" > +"10" )

The answer is simple. Just divide string by 1.
Examples:
"2" > "10" - true
but
"2"/1 > "10"/1 - false
Also you can check if string value really is number:
!isNaN("1"/1) - true (number)
!isNaN("1a"/1) - false (string)
!isNaN("01"/1) - true (number)
!isNaN(" 1"/1) - true (number)
!isNaN(" 1abc"/1) - false (string)
But
!isNaN(""/1) - true (but string)
Solution
number !== "" && !isNaN(number/1)

The alert() wants to display a string, so it will interpret "2">"10" as a string.
Use the following:
var greater = parseInt("2") > parseInt("10");
alert("Is greater than? " + greater);
var less = parseInt("2") < parseInt("10");
alert("Is less than? " + less);

Why doesn't typeof work but isNaN works ?

Why doesn't this block work? I Used isNaN() and that works but not this, why? Javascript is behaving weirdly.
if( (typeof parseInt(returnedArr[count]) == 'number')
{
totalWorth= parseInt(totalWorth)+ parseInt(returnedArr[count]);
//document.write(returnedArr[count]);
}
Code:
function addWorth()
{
var table1= document.getElementById("tableNetWorths");
var rowCount1= table1.rows.length;
//var row1= table1.insertRow(rowCount1);
var arr= [];
for(var count = 0; count < rowCount1; count++)
{
arr.push(table1.rows[count].cells[1].innerHTML);
}
arr.shift();
return arr;
}
function showWorthSum()
{
var returnedArr= addWorth();
//returnedArr.push(addWorth());
totalWorth= 0;
var arrCount= returnedArr.length;
for(var count = 0; count < arrCount; count++)
{
if( (typeof parseInt(returnedArr[count]) == 'number')
{
totalWorth= parseInt(totalWorth)+ parseInt(returnedArr[count]);
//document.write(returnedArr[count]);
}
}
return parseInt(totalWorth);
}
If I use isNaN then that works but not this, why? My array looks like this:
{"100", "200", "asdasdadsa", "1"}

Because typeof NaN is "number":
console.log(typeof NaN);
NaN is a special value* of the number type, not its own type.
You haven't shown your code that uses isNaN, but note that if you pass a string into isNaN, it will be implicitly converted to number before being tested to see if the result of doing that is NaN (as though you had called Number(x) on it, or applied unary + or any of the non-addition math ops [-, *, /, etc.]).
Separately:
Beware that parseInt will happily parse a string that only starts with a number, ignoring the part after it that isn't numeric. For instance, parseInt("123abc") is 123.
Beware that when used without its second argument, parseInt will infer the number base (radix) from the string, so parseInt("0x10") is 16.
When dealing with user input, handling both of those situations intentionally is usually best:
function parseIntStrict(str) {
str = str.trim();
if (!/^\d+$/.test(str)) {
return NaN;
}
return parseInt(str, 10);
}
(Note that doesn't attempt to support scientific notation input; users don't usually input it.)
And for floating point:
function parseFloatStrict(str) {
str = str.trim();
if (!str) {
return NaN;
}
return +str;
}
(That does support scientific notation, but only as a byproduct of only checking for blank strings before handing off to built-in numeric conversion.)
Applying that to your code:
// I assume totalWorth is already a number
var entry = parseIntStrict(returnedArr[count]);
if (!isNaN(entry)) {
totalWorth = totalWorth + entry;
}
* Technically, per the IEEE-754 standard JavaScript uses, NaN is any of a range of values that all mean "not a number."

This is because the values in the array that you consider to be numbers are actually strings. For example, 100 is a number, but '100' is a string. typeof 123 will return 'number', but typeof '123' will return 'string'.
This means that all the values in your array are of type string and your code will not enter the if statement, if you use that approach.
However, since isNaN checks if an element in not a number, your code will work with that.

Comparing 1.3.52 and 1.3.54 as strings and as numbers

I am wondering why the following works:
oldversion = "1.3.52";
newversion = "1.3.54";
if (newversion > oldversion) {
console.log('test');
}
but this does not:
if (1.3.54 > 1.3.52) {
console.log('test');
}
I know that the last example won't work because they are not actual numbers. But I am trying to find out what JavaScript is doing when it encounters a string with a number in it.
This is what I found on W3Schools' JavaScript Comparison and Logical Operators page:
When comparing a string with a number, JavaScript will convert the
string to a number when doing the comparison.
So how come it converts the string to a number and suddenly I am not getting an Uncaught SyntaxError: Unexpected number anymore?

You could use a function which iterates the segments.
function checkVersion(a, b) {
var aa = a.split('.').map(Number),
bb = b.split('.').map(Number),
i,
r = 0,
l = Math.max(aa.length, bb.length);
for (i = 0; !r && i < l; i++) {
r = (aa[i] || 0) - (bb[i] || 0);
}
return r;
}
var oldversion = "1.3.52",
newversion = "1.3.54";
if (checkVersion(newversion, oldversion) > 0) {
console.log('test');
}

As mentioned in the comments, it's actually doing a string compare and not trying to turn anything into numbers.
You can verify this by trying:
var a = "a";
var b = "b";
console.log(a>b) // gives false
var a = "a";
var b = "b";
console.log(b>a) // gives true

As you say, when you compare a number and a string, the string gets transformed into a number. However, if the string contains an invalid number, the result will be NaN. This is funny due to the fact that:
NaN > 15 === false
NaN < 15 === false
So:
"1.3.52" > 1.4 === false
"1.3.52" < 1.4 === false
Obviously (and as you said in your post), comparing 1.3.52 with 1.3.54 will throw an exception because they're not valid numbers.
Why "1.3.52" is interpreted bigger than '1.12.10'?
Strings are compared using Unicode code point order. For example, "Banana" comes before "cherry". "9" is bigger than "80", but because "80" comes before "9" in Unicode order. Thus, "1.3.52" is interpreted as bigger than '1.12.10'.
An easy way to find out order between strings and not getting tricked is using sort. For instance, ["1.3.52", "1.12.10", "1.11.0.0.0"].sort()

#Nina's solution should be the accepted answer, as it will be easier to understand I think. But anyway..
function versionGreaterEqual(newversion, oldversion) {
var ov = oldversion.split('.').map(Number), //credit Nina :)
nv = newversion.split('.').map(Number);
return nv.reduce(function (a,b,i){
return a+=b>=ov[i];
},0)===nv.length;
}
console.log(versionGreaterEqual("1.3.54", "1.3.52")); //true
console.log(versionGreaterEqual("1.3.54", "1.13.52")); //false

Unable to retain leading zeros in javascript

I have
var x = "0100";
parseInt(x); // returns 100;
Is there a way I can retain the leading 0s and yet convert to number in Javascript

Unfortunately it's not possible but I have a solution that can help you, is to define a class from where you can get the value as integer and when you call the toString method it returns the value with leading zeros
function Num ()
{
this.value = arguments[0];
this.val = this.valueOf = function ()
{
return parseInt(this.value);
}
this.toString = function()
{
return this.value;
}
}
Now what you can do is to define a new number like this :
var x = new Num("00011");
x.val() // returns 11
x.toString() // returns "00011"

No.
Numbers don't have leading zeroes; that's a display issue, not a matter of a number's internal representation.
To display the number with leading zeroes, see here.

jQuery Validation, Numeric Value Only

I'm trying to validate a form input value. The function below states is the value of the input is a number below 150, show error. Works as it should. However, I want to add to it. If the value contains ANYTHING other than a numeric value AND/OR is a value under 150, show error...
How can I modify?
if ($('.billboard-height').val() < 150) {
$('.sb-billboardalert').fadeIn(600);
}

Since your more thorough validation should be on the server-side anyway, you could just use parseInt or parseFloat depending on what sort of value you are expecting. Then check if the result is actually a number and that it also meets your constraints:
var number = parseFloat($('.billboard-height').val()); // or parseInt depending on expected input
if (isNaN(number) || number < 150) {
$('.sb-billboardalert').fadeIn(600);
}
EDIT:
Based on your comments, you are entering regex land. I gather you only ever want a natural number (and the way parseInt/parseFloat ignores trailing non-numeric characters like px, em, etc. is not ok). How about:
var val = $('.billboard-height').val();
var number = parseInt(val, 10);
if ( ! val.match(/^[0-9]{3,4}$/) || number < 150) {
$('.sb-billboardalert').fadeIn(600);
}
This should only allow natural numbers 150-9999.

I would suggest using regexes:
var intRegex = /^\d+$/;
var floatRegex = /^((\d+(\.\d *)?)|((\d*\.)?\d+))$/;
var str = $('#myTextBox').val();
if(intRegex.test(str) || floatRegex.test(str)) {
alert('I am a number');
...
}
Or with a single regex as per #Platinum Azure's suggestion:
var numberRegex = /^[+-]?\d+(\.\d+)?([eE][+-]?\d+)?$/;
var str = $('#myTextBox').val();
if(numberRegex.test(str)) {
alert('I am a number');
...
}
ref: checking if number entered is a digit in jquery

Don't forget the radix parameter in parseInt():
if (parseInt($('.billboard-height').val(), 10) < 150) {
It's probably faster than using a regex. Regular expressions are not known for being fast, but they are very powerful. It might be overkill for this scenario.

You can try out HTML5's built in form validation:
<input type="number" min="150">
browser support is still pretty shakey though

Any value from an input or select will be a string in javascript. You need to use parseInt() to use operators like > or <. == can be used if you use it to compare to a string like if ($('.billboard-height').val() == "150")

Try parseInt and isNaN functions for check if value is number and less than 150:
var intVal = parseInt($('.billboard-height').val());
if(!isNaN(intVal)){ //not Number
if (parseInt($('.billboard-height').val()) < 150) { //not less than 150
$('.sb-billboardalert').fadeIn(600);
}
}

If you need to support floating point numbers, you can check if a variable is valid using:
function isNumber (n) {
return !isNaN(parseFloat(n)) && isFinite(n);
}
var val = $('.billboard-height').val();
if (isNumber(val) && parseFloat(val) < 150) {
$('.sb-billboardalert').fadeIn(600);
}
If you only need to support integers, use parseInt(n, 10), where 10 is the base to convert the string to.
var val = parseInt($('.billboard-height').val(), 10);
if (val && val < 150) {
$('.sb-billboardalert').fadeIn(600);
}

// Displays an alert if s contains a non-numeric character.
function alertForNonNumeric(s) {
var rgx = /[^0-9]/;
if (s.search(rgx) !== -1) {
alert("Input contains non-numeric characters!");
}
}
JS Fiddle here
NOTE: If you want to check for negative ints as well, you can add a minus sign to the regex:
function alertForNonNumeric(s) {
var rgx = /[^0-9-]/;
if (s.search(rgx) !== -1) {
alert(s + " contains non-numeric characters!");
}
}

I use this solution, I find it quite ellegant - no alerts, user is effectively unable to enter non numeric characters.
This is jQuery example:
function digitsOnly(){
// extract only numbers from input
var num_val = $('#only_numbers').val().match(/\d+/);
$('#only_numbers').val(num_val);
}
Your html:
<input type="text" name="only_numbers" id="only_numbers" on oninput="digitsOnly();"/>