javascript Number validations

Question

I need to check if a number entered contain

1.more than two digit after decimal

2.decimal at first place (ex:.2345)

3.decimal at last place (ex:2345.)

How to do this using javascript.

• Ash Burlaczenko: How can a NUMBER have a decimal at the front and end? I think your meant to ask about strings.
• user447356: Is this part of form validation?

Answer 1

len = number.length;
pos = number.indexOf('.');
if (pos == 0)
{
 //decimal is at first place
}
if (pos == len - 1)
{
 //decimal is at last place
}
if (pos == len - 3)
{
 //more than two digit after decimal
}

• jwueller: .length is a property, not a method. Nice and fast apprach, however.
• kzh: Probably should use else...if so as to not test multiple times.
• Mark Baijens: use pos < len - 3. Now it can have only 2 decimals.

Answer 2

var reg = /\d+(?:\.\d{2,})?/;
if ( reg.test(number) )
 alert('Correct format!');

Not sure whether you'd allow decimals only (i.e. without the period) but if, that regexp should be sufficient.

Good luck.

• jwueller: Why would he need luck? Is your code that fragile? ;) +1 for the correct answer.
• aefxx: Good luck with his effort to validate user input, that is.
• jwueller: You're right about that. One needs to be very careful with user input.

Answer 3

function check_number(number) {
 var my_number = String(number);
 var place = my_number.indexOf(".");
 if(place == 0) return "first";
 else if(place == (my_number.length - 1)) return "last";
 else if(place == (my_number.length - 3)) return "third to last";
}

• kzh: @Shakti Singh, you beat me to the answer.

Answer 4

var number = "3.21";
if(/[0-9]{1,}\.[0-9]{2,}/.test(number)) {
 //valid
}

• jwueller: I think number should be a string here. Besides that, .test() is a method of the RegExp object. You should use .match() or modify your code so that your regular expression is in front.
• Mark Baijens: Ah yes, thanks for pointing that out. Can you only pass a regex on strings in js?
• jwueller: I am not sure if i understand what you mean, but .match() is a method of String. You can use it to do it the other way around: "some string".match(/some/)
• Mark Baijens: Does it matter? Is match better compared to test?