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Why parseInt() works like this?
I have an issue with parseInt() returning 0 unexpectedly, here's a sample:
parseInt('-06') = -6
parseInt('-07') = -7
parseInt('-08') = 0
Why is the result 0? Same if I keep going down (-09, -10, ect). The format of the string comes from my framework so I need to deal with it. Thanks!
You need to pass a radix parameter when you use parseInt
parseInt('-08', 10);
When you don't, and when the string you're parsing has a leading zero, parseInt produces different results depending on your browser. The most common issue is that the string will be treated as a base-8 number, which is what you're seeing.
That's why this worked for '-06' and '-07'—those are both valid base-8 numbers. Since '-08' isn't a valid base-8 number, the parse failed, and 0 was returned.
From MDN
radix
An integer that represents the radix of the above mentioned
string. While this parameter is optional, always specify it to
eliminate reader confusion and to guarantee predictable behavior.
Different implementations produce different results when a radix is
not specified.
Also note that you can use the unary + operator to convert these strings to numbers:
var str = '-08';
var num = +str;
console.log(num);
//logs -8
DEMO
You could also try this:
'-06' * 1 = -6
'-07' * 1 = -7
'-08' * 1 = -8
this is a bug in firefox, use parseFloat instead .get more detaile about this bug here.
check parseFloat result HERE.
Related
I have just observed that the parseInt function doesn't take care about the decimals in case of integers (numbers containing the e character).
Let's take an example: -3.67394039744206e-15
> parseInt(-3.67394039744206e-15)
-3
> -3.67394039744206e-15.toFixed(19)
-3.6739e-15
> -3.67394039744206e-15.toFixed(2)
-0
> Math.round(-3.67394039744206e-15)
0
I expected that the parseInt will also return 0. What's going on at lower level? Why does parseInt return 3 in this case (some snippets from the source code would be appreciated)?
In this example I'm using node v0.12.1, but I expect same to happen in browser and other JavaScript engines.
I think the reason is parseInt converts the passed value to string by calling ToString which will return "-3.67394039744206e-15", then parses it so it will consider -3 and will return it.
The mdn documentation
The parseInt function converts its first argument to a string, parses
it, and returns an integer or NaN
parseInt(-3.67394039744206e-15) === -3
The parseInt function expects a string as the first argument. JavaScript will call toString method behind the scene if the argument is not a string. So the expression is evaluated as follows:
(-3.67394039744206e-15).toString()
// "-3.67394039744206e-15"
parseInt("-3.67394039744206e-15")
// -3
-3.67394039744206e-15.toFixed(19) === -3.6739e-15
This expression is parsed as:
Unary - operator
The number literal 3.67394039744206e-15
.toFixed() -- property accessor, property name and function invocation
The way number literals are parsed is described here. Interestingly, +/- are not part of the number literal. So we have:
// property accessor has higher precedence than unary - operator
3.67394039744206e-15.toFixed(19)
// "0.0000000000000036739"
-"0.0000000000000036739"
// -3.6739e-15
Likewise for -3.67394039744206e-15.toFixed(2):
3.67394039744206e-15.toFixed(2)
// "0.00"
-"0.00"
// -0
If the parsed string (stripped of +/- sign) contains any character that is not a radix digit (10 in your case), then a substring is created containing all the other characters before such character discarding those unrecognized characters.
In the case of -3.67394039744206e-15, the conversion starts and the radix is determined as base 10 -> The conversion happens till it encounters '.' which is not a valid character in base 10 - Thus, effectively, the conversion happens for 3 which gives the value 3 and then the sign is applied, thus -3.
For implementation logic - http://www.ecma-international.org/ecma-262/5.1/#sec-15.1.2.2
More Examples -
alert(parseInt("2711e2", 16));
alert(parseInt("2711e2", 10));
TO note:
The radix starts out at base 10.
If the first character is a '0', it switches to base 8.
If the next character is an 'x', it switches to base 16.
It tries to parse strings to integers. My suspicion is that your floats are first getting casted to strings. Then rather than parsing the whole value then rounding, it uses a character by character parsing function and will stop when it gets to the first decimal point ignoring any decimal places or exponents.
Some examples here http://www.w3schools.com/jsref/jsref_parseint.asp
parseInt has the purpose of parsing a string and not a number:
The parseInt() function parses a string argument and returns an
integer of the specified radix (the base in mathematical numeral
systems).
And parseInt calls the function ToString wherein all the non numerical characters are ignored.
You can use Math.round, which also parses strings, and rounds a number to the nearest integer:
Math.round("12.2e-2") === 0 //true
Math.round("12.2e-2") may round up or down based on the value. Hence may cause issues.
new Number("3.2343e-10").toFixed(0) may solve the issue.
Looks like you try to calculate using parseFloat, this will give you the correct answer.
parseInt as it says, returns an integer, whereas parseFloat returns a floating-point number or exponential number:
parseInt(-3.67394039744206e-15) = -3
parseFloat(-3.67394039744206e-15) = -3.67394039744206e-15
console.log('parseInt(-3.67394039744206e-15) = ' , parseInt(-3.67394039744206e-15));
console.log('parseFloat(-3.67394039744206e-15) = ',parseFloat(-3.67394039744206e-15));
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Workarounds for JavaScript parseInt octal bug
Parsing a string using parseInt method returns invalid output .
Code :
parseInt("08");
Excepted Output :
8
Real Output :
0
Code [This returns output correctly] :
parseInt("8")
Output :
8
Why it happens ?
You need to specify the base:
parseInt("08",10); //=>8
Otherwise JavaScript doesn't know if you are in decimal, hexadecimal or binary.
(This is a best practise you should always use if you use parseInt.)
Also see Number:
Number("08"); // => 8
What is the difference between parseInt() and Number()?
What is the difference between parseInt(string) and Number(string) in JavaScript?
You should tell parseInt its 10 based:
parseInt("08", 10);
JavaScript parseInt() Function
If the radix parameter is omitted, JavaScript assumes the following:
If the string begins with "0x", the radix is 16 (hexadecimal)
If the string begins with "0", the radix is 8 (octal). This feature is
deprecated If the string begins with any other value, the radix is 10
(decimal)
http://jsfiddle.net/YChK5/
Strings with a leading zero are often interpreted as octal values. Since octal means, that only numbers from 0-7 have a meaning, "08" is converted to "0". Specify the base to fix this problem:
parseInt("08", 10); // base 10
As usual, the MDN is a good source of information:
https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/parseInt#Octal_Interpretations_with_No_Radix
I ran JSLint on this JavaScript code and it said:
Problem at line 32 character 30: Missing radix parameter.
This is the code in question:
imageIndex = parseInt(id.substring(id.length - 1))-1;
What is wrong here?
It always a good practice to pass radix with parseInt -
parseInt(string, radix)
For decimal -
parseInt(id.substring(id.length - 1), 10)
If the radix parameter is omitted, JavaScript assumes the following:
If the string begins with "0x", the radix is 16 (hexadecimal)
If the string begins with "0", the radix is 8 (octal). This feature is deprecated
If the string begins with any other value, the radix is 10 (decimal)
(Reference)
To avoid this warning, instead of using:
parseInt("999", 10);
You may replace it by:
Number("999");
Note that parseInt and Number have different behaviors, but in some cases, one can replace the other.
I'm not properly answering the question but, I think it makes sense to clear why we should specify the radix.
On MDN documentation we can read that:
If radix is undefined or 0 (or absent), JavaScript assumes the
following:
[...]
If the input string begins with "0", radix is eight (octal) or 10 (decimal). Exactly which radix is chosen is implementation-dependent.
ECMAScript 5 specifies that 10 (decimal) is used, but not all browsers support this yet. For this reason always specify a radix
when using parseInt.
[...]
Source: MDN parseInt()
You can turn off this rule if you wish to skip that test.
Insert:
radix: false
Under the "rules" property in the tslint.json file.
It's not recommended to do that if you don't understand this exception.
Adding the following on top of your JS file will tell JSHint to supress the radix warning:
/*jshint -W065 */
See also: http://jshint.com/docs/#options
Prior to ECMAScript 5, parseInt() also autodetected octal literals, which caused problems because many developers assumed a leading 0 would be ignored.
So Instead of :
var num = parseInt("071"); // 57
Do this:
var num = parseInt("071", 10); // 71
var num = parseInt("071", 8);
var num = parseFloat(someValue);
Reference
Simply add your custom rule in .eslintrc which looks like that
"radix": "off"
and you will be free of this eslint unnesesery warning.
This is for the eslint linter.
I solved it with just using the +foo, to convert the string.
Keep in mind it's not great for readability (dirty fix).
console.log( +'1' )
// 1 (int)
You can also simply add this line right above your parseInt line:
// eslint-disable-next-line
This will disable eslint check for the next line. Use this if you only need to skip one or two lines.
Just put an empty string in the radix place, because parseInt() take two arguments:
parseInt(string, radix);
string
The value to parse. If the string argument is not a string, then it is converted to a string (using the ToString abstract operation). Leading whitespace in the string argument is ignored.
radix
An integer between 2 and 36 that represents the radix (the base in mathematical numeral systems) of the above-mentioned string. Specify 10 for the decimal numeral system commonly used by humans. Always specify this parameter to eliminate reader confusion and to guarantee predictable behavior. Different implementations produce different results when a radix is not specified, usually defaulting the value to 10.
imageIndex = parseInt(id.substring(id.length - 1))-1;
imageIndex = parseInt(id.substring(id.length - 1), '')-1;
Instead of calling the substring function you could use .slice()
imageIndex = parseInt(id.slice(-1)) - 1;
Here, -1 in slice indicates that to start slice from the last index.
Thanks.
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
Workarounds for JavaScript parseInt octal bug
EXTREMELY confused here.
parseInt("09") = 0
but
parseInt("9") = 9
Why is the prefixed zero not just stripped out?
alert(parseInt("01")); = 1
.. rage quit
Because that is treated as octal format, by default. If you want to get 9, you must add number base you want, and thats 10, not 8 (for octal), so call:
parseInt("09", 10);
A.7. parseInt
parseInt is a function that converts a string into an integer. It stops when it sees a nondigit, so
parseInt("16") and parseInt("16 tons") produce the same result. It would be nice if the
function somehow informed us about the extra text, but it doesn't.
If the first character of the string is 0, then the string is evaluated in base 8 instead of base 10. In base 8, 8 and
9 are not digits, so parseInt("08") and parseInt("09") produce 0 as their result. This error causes
problems in programs that parse dates and times. Fortunately, parseInt can take a radix parameter, so that
parseInt("08", 10) produces 8. I recommend that you always provide the radix parameter.
"JavaScript: The Good Parts by Douglas Crockford. Copyright 2008 Yahoo! Inc.,
978-0-596-51774-8."
this the reasons:
If the string begins with "0x", the radix is 16 (hexadecimal)
If the string begins with "0", the radix is 8 (octal). This feature is deprecated
If the string begins with any other value, the radix is 10 (decimal)
http://www.w3schools.com/jsref/jsref_parseInt.asp
Do
parseInt("09", 10)
To specify base 10.
Edit: To clarify, a number prefixed by a zero will be assumed to be of octal notation, and "09" isn't a valid octal number.
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)