Why can't we use integer keys in dot expression to access property values ?
var obj = {1: 'one', two: '2'}
console.log(obj.1) // error
console.log(obj.two)
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3I think due to the limitation of naming convention of javascript variable.Abhisek Malakar– Abhisek Malakar2015-04-27 06:03:18 +00:00Commented Apr 27, 2015 at 6:03
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1 is represented as string internally.m_allaudin– m_allaudin2015-04-27 06:06:29 +00:00Commented Apr 27, 2015 at 6:06
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3 Answers
In case of dot notation to access a value, the property key must be a valid identifier
In this code, property must be a valid JavaScript identifier, i.e. a sequence of alphanumerical characters, also including the underscore ("_") and dollar sign ("$"), that cannot start with a number. For example, object.$1 is valid, while object.1 is not.
You can use bracket notation in this case
obj['1']
Spec: Property Accessors
2 Comments
rooby
The last link is broken.
mplungjan
@rooby I changed it to ecma-international.org/ecma-262/6.0/#sec-property-accessors
Adding to @Arun P Johny' s answer
we can use obj['1'] with quotes or obj[1] without quotes in case of integer.
where as accessing obj['two'] will work but obj[two] will throw an error if there is no variable/constant as two.
Comments
It is a JavaScript base princible which says variables cannot start with a number. Over here the property is a variable and hence it cannot start with a number.
You can check more about variable definition rules here
Hope this helps.
3 Comments
rooby
This link is broken.
mplungjan
Whilst this may theoretically answer the question, it would be preferable to include the essential parts of the answer here, and provide the link for reference since it is now dead
Bergi
Property names are not variables.