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toString(16) with leading zeroes [duplicate]

This question already has answers here:
How can I pad a value with leading zeros?
(76 answers)
Closed 9 years ago.
When you convert a small number to a hexadecimal representation, you need leading zeroes, because toString(16) will return f for 15, instead of 00000f. Usually I will use the loop like this:
var s = X.toString(16); while (s.length < 6) s = '0' + s
is there a better way in JavaScript?
UPD: The answer suggested answer How can I create a Zerofilled value using JavaScript? is not what I am looking for, I look for a very short code, that is suited specifically for 24 bit integers converted to a hexadecimal looking strings.

How about
('00000'+(15).toString(16)).substr(-5)

Maybe this:
var s = X.toString(16);
s = "000000".substr(0, 6 - s.length) + s;

Effect of x = +x in JavaScript [duplicate]

This question already has answers here:
Coerce to number
(4 answers)
Closed 9 years ago.
Going though the asm.js documentation I've observed this strange (to me at least, quite new to JS) snippet all over the sample code:
function test(x) {
x = +x; // THIS
...
return +(x*y);
}
What is the purpose of the + on the first line?

Its simply used for casting a value with another type to number. Additonally it will return NaN if the value after that + symbol could not get converted into a number.
FIDDLE
From the book Javascript and Jquery - The Missing Maunal
var numOfShoes = '2';
var numOfSocks = 4;
var totalItems = +numOfShoes + numOfSocks;
Adding a + sign before a variable (make sure there’s no space between the two) tells
the JavaScript interpreter to try to convert the string to a number value—if the string
only contains numbers like “2”, you’ll end up with the string converted to a number.
In this example, you end up with 6 (2 + 4). Another technique is to use the Number()
command like this:
var numOfShoes = '2';
var numOfSocks = 4;
var totalItems = Number(numOfShoes) + numOfSocks;
Number() converts a string to a number if possible. (If the string is just letters and not
numbers, you get the NaN value to indicate that you can’t turn letters into a number.)

Perhaps I am reading this wrong but from the specs http://asmjs.org/spec/latest/#parameter-type-annotations
is that casting it as a double?

How do I add a random number to a Stored variable at the results as a number, not 2 strings added together? [duplicate]

This question already has answers here:
javascript calculation formula is not working
(2 answers)
Closed 10 years ago.
So here is a dorky experiment I put together basically trying to generate a D&D style attack roll with a modifier. I want to add the numbers, but javascript keeps adding the numbers as strings. I'm not sure how to get the basic math done..... Here is my code-
function battle()
{
var CS = document.battleForm.playerCS.value;
var D20 = Math.ceil(Math.round(Math.random() * 20))
var attackRoll = CS + D20
if (isNaN(CS))
{
alert ("please provide your Combat Score!")
return
}
if (CS != '')
{
document.battleForm.enemyCS.value = attackRoll
}
}

To ensure two numbers are added together, try:
var num3 = +num1 + (+num2);
This could be preferred over the use of parseInt or parseFloat for two reasons:
+ will convert any number (meaning, you don't need a different method for an integer and a float)
+ will fail if either value are not convertible. parseInt and parseFloat ignore any trailing text in the variable. So for example, parseInt("10px", 10) results in 10, while (+"10px") results in NaN.
It's up to you what you want to use.

var CS = parseInt(document.battleForm.playerCS.value, 10); // or parseFloat if you expect float number
The value of any form text is a string, so you need to convert it to number.

Regular expression between two numeric values [duplicate]

This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
how to match a number which is less than or equal to 100?
i need a regular expression between these two values 1000 <= x <= 500000 im trying with this one that i constructed but doesnt seem to work
/(1[8-9]|[8-9]|[8-9]|5[0-9]|[0-9]|[0-9]|[0-9]|[0-9])/
Any ideas? thanks in advance!

Is there a particular reason you don't just test the numbers as numbers?
var yourNum = parseInt(yourString, 10); // use parseFloat if it has decimals
if (yourNum >= 1000 && yourNum <= 500000) {
// success
} else
// fail
}

\b([1-9][0-9]{3,4}|[1-4][0-9]{5}|500000)\b

Match the cases 1000-9999, 10000-99999, 100000-499999 or 500000:
([1-9]\d{3}|[1-9]\d{4}|[1-4]\d{5}|500000)
Or combining the two first:
([1-9]\d{3,4}|[1-4]\d{5}|500000)

javascript problem with parseint [duplicate]

This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
Workarounds for JavaScript parseInt octal bug
I am trying to parse an integer number.
a = parseInt("0005") <- gives 5
a = parseInt("0008") <- gives 0
Can someone explain what's happening? It doesn't make any sense to me.

When parseInt has a leading 0 and a radix parameter isn't specified, it assumes you want to convert the number to octal. Instead you should always specify a radix parameter like so:
a = parseInt("0008", 10) // => 8

Numbers starting with 0 are parsed as octal by parseInt, unless you specify a radix to use.
You can force parseInt to parse as decimal by doing
a = parseInt("0008", 10)