javascript - What's the difference when defining var as 0.5 compared to .5? - Stack Overflow

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I'm curious, I have programmed JavaScript already few years but sometimes I get confused when I see the following variable declarations: (ofc. those could be any other numbers as well).

var exampleOne = 0.5;
var exampleTwo = .5;

What is the difference between these two, or is there any? Are there some sort of hidden benefits which I clearly don't understand?

I'm curious, I have programmed JavaScript already few years but sometimes I get confused when I see the following variable declarations: (ofc. those could be any other numbers as well).

var exampleOne = 0.5;
var exampleTwo = .5;

What is the difference between these two, or is there any? Are there some sort of hidden benefits which I clearly don't understand?

• javascript

Share Improve this question Follow edited Feb 18, 2014 at 2:10 Felix Kling 818k181181 gold badges1.1k1.1k silver badges1.2k1.2k bronze badges asked Feb 18, 2014 at 1:50 Mauno VähäMauno Vähä 9,78833 gold badges3535 silver badges5555 bronze badges 3

• Some people find the first version easier to read, but there's no difference to the puter. – Barmar Commented Feb 18, 2014 at 1:52
• Relevant section in the spec: es5.github.io/#x7.8.3 (DecimalLiteral) – Felix Kling Commented Feb 18, 2014 at 1:52
• The difference is one character. – Ja͢ck Commented Feb 18, 2014 at 1:54

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2 Answers 2

Sorted by: Reset to default 4

To quote the specification:

0.5 matches the rule DecimalLiteral :: DecimalIntegerLiteral . DecimalDigits which is evaluated as (MV means mathematical value):

The MV of DecimalLiteral :: DecimalIntegerLiteral . DecimalDigits is the MV of DecimalIntegerLiteral plus (the MV of DecimalDigits times 10^–n), where n is the number of characters in DecimalDigits.

.5 matches the rule DecimalLiteral :: . DecimalDigits which is evaluated as

The MV of DecimalLiteral :: . DecimalDigits is the MV of DecimalDigits times 10^–n, where n is the number of characters in DecimalDigits.

So you can see that the only difference is that the value of the digits preceding the . are added to the final value. And adding 0 to a value doesn't change the value.

There is no difference.

The Numeric Literals are parsed equivalently - that is, both 0.5 and .5 (as would .50) represent the same number. (Unlike most other languages, JavaScript has only one kind of number.)

I prefer to always include the [optional] leading 0 before the decimal.

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