How to prevent removing decimal point when parsing JSON?

Question

If you do this...

var parsed = JSON.parse('{"myNum":0.0}') ;

Then when you look at parsed.myNum, you just get 0. (Fair enough.)

If you do parsed.myNum.toString(), you get "0".

Basically, I'm looking for a way to turn this into the string "0.0".

Obviously, in real life I don't control the JSON input, I get the JSON from a web service... I want to parse the JSON using the browser's JSON parser, and to be able to recognise the difference between the number values 0 and 0.0.

Is there any way to do this, short of manually reading the JSON string? That's not really possible in this case, I need to use the browser's native JSON parser, for speed. (This is for a Chrome extension by the way; no need to worry about it working in other browsers.)

Solution 1

There's no way to get the number of digits from JSON.parse or eval. Even if IBM's decimal proposal had been adopted by the EcmaScript committee, the number is still going to be parsed to an IEEE 754 float.

Take a look a http://code.google.com/p/json-sans-eval/source/browse/trunk/src/json_sans_eval.js for a simple JSON parser that you can modify to keep precision info.

Solution 2

If 0.0 is not enclosed in quotes in your JSON (i.e. it's a number and not a string), then there's no way to distinguish it from 0, unless you write your own JSON parser.

Solution 3

... parsed.myNum.toFixed( 1 ) ...

where 1 is number of decimal places

Edit: parsed.myNum is number, parsed.myNym.toFixed( 1 ) would be string

Edit2: in this case you need to pass value as string {"myNum":'0.0'} and parsed when calculations is needed or detect decimal separator, parsed number, and use decimal separator position when string is needed

Comments

[Mike Samuel]

JavaScript doesn't have distinct integer and floating point number types. The language specification says that coercing a number that has no fraction to a string will drop the decimal point. Use one of the custom formatting methods like the one bensiu suggests.

[Peter Hedberg]

Actually, mathematically there is a difference between 0 and 0.0 :)

[Felix Kling]

What differences does it make? 0 is 0.0 is 0.00000000000....

[callum]

@Felix Kling: Yes, I know 0 is mathematically the same number as 0.0 :) But imagine a situation where a web server serves either 0 or 0.0, depending on how it's stored in the database (as an integer or as a float). And I want to be able to make that distinction in JavaScript.

[callum]

Sorry, I need to be able to work out if the number is 0 or 0.0. (Or 0.00 for that matter.) I want to be able to get the number with the correct number of digits after the decimal point, exactly as it appears in the JSON string.

[Mike Samuel]

This is your best bet, but it will still not give you a decimal point for numbers large enough that they are normally displayed in scientific notation. E.g. 1e30.toFixed(1) === '1e30'

[callum]

Thanks, perfect answer. I'll have a look at that parser.

[Lee]

It does matter when trying to match them both in HTML.