Using integer keys with dot notation to access property in javascript objects - Stack Overflow

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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)

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)

• javascript
• object

Share Improve this question Follow asked Apr 27, 2015 at 6:01 bilal_azambilal_azam 4,81044 gold badges3838 silver badges6969 bronze badges 2

• 3 I think due to the limitation of naming convention of javascript variable. – Abhisek Malakar Commented Apr 27, 2015 at 6:03
• 1 is represented as string internally. – bilal_azam Commented Apr 27, 2015 at 6:06

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3 Answers 3

Sorted by: Reset to default 13

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

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.

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.

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