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Validate particular range using regex

I want validate text box with particular range having format like :
1-99
I am using regex :
/^(?:100|[1-9]\d|\d)-(?:100|[1-9]\d|\d)$/
It works for me but little problem that is it accept this:
55-50
And it shouldn't, this is wrong.
how can I correct this?

As it has been told early regexp is not the method for validating ranges. The better way is to use if/else statements. But you are not restricted in usage of regexp for validating input string on the particular format.
F.i., if you'd like to enable the end user to enter the range in the format number1-number2, you could check the string for compliance to this format and check its parts for complaince to the condition number1 <= number2. If all these checks are done you could do something useful or decline, if checks are fail.
function validRange(rangeStr, min, max) {
var m = rangeStr.match(/^([0-9]+)-([0-9]+)$/);
if ( m && m[1] >= min && m[2] <= max && m[1] <= m[2] ) {
return true;
}
return false;
}
var s = '1-99';
var s = '55-50';
if ( validRange(s, 1, 99) ) {
// do something useful
}
The code above is just skeleton for the further improvements but it can be used now. But the code could be too complicated, if you or your customers will request to implement something more complex like ability to enter single number, lists of numbers (separated with comma, semicolons etc), mixed ranges or any combination of all of them.

Because you need to check validation between the both number you have to use logical operations to check if the forst number is less than second, so you couldn't use regex in this case instead use if/else statement :
var input = "55-50";
if(input.indexOf('-')){
var input_arr = input.split('-');
if(input_arr.length==2 && parseInt(input_arr[0])<parseInt(input_arr[1]))
alert("Accepted");
else
alert("Not accepted");
}

remove decimal in javascript

I want to remove decimal from number in javascript:
Something like this:
12 => 12
12.00 => 1200
12.12 => 1212
12.12.12 => error: please enter valid number.
I can not use Math.round(number). Because, it'll give me different result. How can I achieve this? Thanks.

The simplest way to handle the first three examples is:
function removeDecimal(num) {
return parseInt(num.toString().replace(".", ""), 10);
}
This assumes that the argument is a number already, in which case your second and fourth examples are impossible.
If that's not the case, you'll need to count the number of dots in the string, using something like (trick taken from this question):
(str.match(/\./g) || []).length
Combining the two and throwing, you can:
function removeDecimal(num) {
if ((num.toString().match(/\./g) || []).length > 1) throw new Error("Too many periods!");
return parseInt(num.toString().replace(".", ""), 10);
}
This will work for most numbers, but may run into rounding errors for particularly large or precise values (for example, removeDecimal("1398080348.12341234") will return 139808034812341230).
If you know the input will always be a number and you want to get really tricky, you can also do something like:
function removeDecimal(num) {
var numStr = num.toString();
if (numStr.indexOf(".") === -1) return num;
return num * Math.pow(10, numStr.length - numStr.indexOf(".") - 1);
}

You can use the replace method to remove the first period in the string, then you can check if there is another period left:
str = str.replace('.', '');
if (str.indexOf('.') != -1) {
// invalid input
}
Demo:
function reformat(str) {
str = str.replace('.', '');
if (str.indexOf('.') != -1) {
return "invalid input";
}
return str;
}
// show in Stackoverflow snippet
function show(str) {
document.write(str + '<br>');
}
show(reformat("12"));
show(reformat("12.00"));
show(reformat("12.12"));
show(reformat("12.12.12"));

How about number = number.replace(".", ""); ?

parseInt doesn't work

in my current source code textbox value is 1.
when I try alert(isNaN(obj.text()) it returns false that is expected but after parseInt when I write alert(a); it returns NaN
minus.click(function () {
var a = 1; if (!isNaN(obj.text())) a = parseInt(obj.text());
if (a > 1) a -= 1; obj.text(a);
});
what is the problem?
Edit: this is the full code:
<input type="text" class="basket-txt" value="1" />
jQuery.fn.basket = function (options) {
var defaults = {
}
options = jQuery.extend(defaults, options);
this.each(function () {
var $this = $(this);
$this.height(32).css({ 'line-height': '32px', 'font-weight': 'bold', 'width':'40px', 'text-align':'center', });
var tbl = $('<table border="0" style="border-spacing:0px;float:left;">').appendTo($this.parent());
var tr1 = $('<tr>').appendTo(tbl);
var plus = $('<div class="basket-plus">');
$('<td>').append(plus).appendTo(tr1);
$('<td>').append($this).appendTo(tr1);
var minus = $('<div class="basket-minus">');
$('<td>').append(minus).appendTo(tr1);
var tr2 = $('<tr>').appendTo(tbl);
$('<td>').appendTo(tr2);
$('<td>').appendTo(tr2).append($('<div>').addClass('add-to-basket'));
$('<td>').appendTo(tr2);
$this.keypress(function (e) { if (e.which < 48 || e.which > 57) e.preventDefault(); });
minus.click(function () {
var a = 1; if (!isNaN($this.text())) a = parseInt($this.text());
if (a > 1) a -= 1; $this.text(a);
});
plus.click(function () {
var a = 1; if (!isNaN($this.text())) a = parseInt($this.text());
if (a < 1000000) a += 1; $this.text(a);
});
});
}
actually I knew I could correct the code and it would work my concern was to understand why isNaN returns false but parseInt returns NaN

The jQuery text() method will take all the descendent text nodes of an element and combine them into a single string.
An input element can't have descendant nodes of any kind. Its current value is exposed via the value property, which you can read with the val() method in jQuery.
You shouldn't use parseInt without a radix, especially with free form input. You might get octal or hex data instead of a decimal.
parseInt($this.val(), 10)

You get the value of an <input> with .val(), not .text().
The isNaN() function returns false for isNaN(""). Why? Because when "" (the empty string) is converted to a number, it's 0. Pass a non-number to isNaN() and the first thing it does is coerce the value into a number.
It's kind-of pointless to try isNaN() before parseInt() anyway, since parseInt() will tell you when it can't parse a nice-looking integer. Note however that parseInt() doesn't care if there's garbage at the end of the input.
If you want to convert a string to a number when it's a valid string representation of a number, and NaN when it isn't, you can use
var myNumber = +myString;
That'll accept numbers with fractional parts and exponents too, so you'd have to either truncate that to just an integer or check to see if it is one:
var myNumber = +myString;
if (isNaN(myNumber))
// not a valid number
else if (myNumber !== Math.floor(myNumber))
// not an integer
else
// yaay!

minus.click(function () {
// let's parse the integer first
var num = parseInt( obj.val(), 10 );
// then later, we can check if it's NaN
if ( !isNaN(num) && num > 1 ) {
num -= 1;
obj.val(num);
}
});
actually I knew I could correct the code and it would work my concern was
to understand why isNaN returns false but parseInt returns NaN
isNaN doesn't work the way it should. There is type coercion going on.
isNaN will convert the value to a number first. An empty string will be converted to a 0
Number("") === 0; // true
0 is obviously not NaN, so it returns false.
parseInt doesn't do type coercion, it parses the value differently.
Check this question and this other question for reference.

parseInt returns NaN when the first non-whitespace character cannot be converted to a number.

Novice Javascript query about bad input

I am making a simple tip calculator to help myself learn Javascript. The problem I can't solve is how to compensate for "bad input".
In the code below if the user prefaces the numeric input amount with a dollar sign $, the result is NAN.
function tipAmount(){
var dinner=prompt("How much was dinner?");
result = dinner*.10;
alert("Your tip is " +"$"+result );
}
How do I fix that.

You can try to parse out the numeric value with a regular expression:
var match = dinner.match(/\d+\.?\d*/); // parse with a regular expression
if(!match) { // not able to parse
alert("wrong");
}
var price = +match[0]; // convert to a number
result = price * .10;
The regular expression /\d+\.?\d*/ means: one or more digits, and possibly a dot with other digits following. This means that if e.g. dinner is "$1.23", price will be the number 1.23. The same goes for "$ 1.23" or "1.23 dollar" etc - the number will be parsed out with the pattern defined by the regular expression.

The simplest way would be to parse the input into a float, and see if NaN is returned.
if (isNaN(parseFloat(dinner)))
alert("Bad Input")
Just note that 45.2WWW will return 45.2, and so the above will pass.
If you want to make sure what the user typed in is exactly a number, you could do something like this:
var str = '3.445';
var num = parseFloat(str);
if (isNaN(num) || str.length !== num.toString().length)
alert("Bad Input");

try to parse the input as float or integer depending on your needs:
var dinner = parseFloat(prompt("How much was dinner?"));
or
var dinner = parseInt(prompt("How much was dinner?"));
this functions return 0 whether they unable to parse the input as number

Given your approach of using alerts, the following will work:
function tipAmount() {
var dinner=prompt("How much was dinner?");
//convert "dinner" to a number, stripping out any non numeric data
dinner = Number(dinner.replace(/[^0-9\.]+/g,""));
//any unknown data will convert to 0
if(dinner <= 0) {
alert("Please enter a valid amount");
return false;
}
var result = dinner*.10;
alert("Your tip is " +"$"+result );
return true;
}
Please tip more!

Just check if the value is numeric - Javascript's isNaN:
if (isNaN(dinner)) {
alert('Bad number, bub.');
return;
}

Or, if you want to allow users to type in both - just number or an amount with $ at the beginning, you can check for first char:
if( dinner.charAt(0) == '$' )
{
dinner = dinner.substring(1);
}
This way, whenever user types $, your app will just remove it. If they type a normal number it will calculate the tip for you...

Round the value in Javascript

I have scenario where if user enters for example 000.03, I want to show the user it as .03 instead of 000.03. How can I do this with Javascript?

You can use a regular expression:
"000.03".replace(/^0+\./, ".");
Adjust it to your liking.

This actually is trickier than it first seems. Removing leading zero's is not something that is standard Javascript. I found this elegant solution online and edited it a bit.
function removeLeadingZeros(strNumber)
{
while (strNumber.substr(0,1) == '0' && strNumber.length>1)
{
strNumber = strNumber.substr(1);
}
return strNumber;
}
userInput = "000.03";
alert(removeLeadingZeros(userInput));

How about:
function showRounded(val) {
var zero = parseInt(val.split('.')[0],10) === 0;
return zero ? val.substring(val.indexOf('.')) : val.replace(/^0+/,'') );
}
console.log(showRounded('000.03')); //=> ".03"
console.log(showRounded('900.03')); //=> "900.03"
console.log(showRounded('009.03')); //=> "9.03"
Or adjust Álvaro G. Vicario's solution to get rid of leading zero's into:
String(parseFloat("090.03")).replace(/^0+\./, ".")

This function will take any string and try to parse it as a number, then format it the way you described:
function makePretty(userInput) {
var num,
str;
num = parseFloat(userInput); // e.g. 0.03
str = userInput.toString();
if (!isNaN(num) && str.substring(0, 1) === '0') {
str = str.substring(1); // e.g. .03
} else if (isNaN(num)) {
str = userInput; // it’s not a number, so just return the input
}
return str;
}
makePretty('000.03'); // '.03'
makePretty('020.03'); // '20.03'
It you feed it something it cannot parse as a number, it will just return it back.
Update: Oh, I see If the single leading zero needs to be removed as well. Updated the code.

Assuming your input's all the same format, and you want to display the .
user = "000.03";
user = user.substring(3);

You can convert a string into a number and back into a string to format it as "0.03":
var input = "000.03";
var output = (+input).toString(); // "0.03"
To get rid of any leading zeroes (e.g. ".03"), you can do:
var input = "000.03";
var output = input.substr(input.indexOf(".")); // ".03"
However, this improperly strips "20.30" to ".30". You can combine the first two methods to get around this:
var input = "000.03";
var output = Math.abs(+input) < 1 ?
input.substr(input.indexOf(".")) :
(+"000.03").toString();