Why array cannot be accessed like given below?

Question

Below code returns true. If that is the case why does 4th line in the code error out?

var x = ['a', 'e', 'f'];
x[2];
alert('2' in x);
alert(x.2);

I bet it's the same reason why you can't have something like var 2nd = "second". Identifiers can't start with a number. — Arturo Torres Sánchez
– Arturo Torres Sánchez, Commented Dec 2, 2014 at 5:32

JLRishe · Accepted Answer · 2014-12-02 05:43:16Z

2

The only property names you can access with the dot syntax are those that conform to JavaScript's rules for identifier names (first character is a letter, _, or $, and remaining characters are letters, numbers, _, or $).

What you have there is a syntax error, and that's why it errors out.

From MDN:

Dot notation

get = object.property;
object.property = set;

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 the square bracket notation to access a property with any name, so either of the following will return the item you want:

x[2];
x["2"];

edited Dec 2, 2014 at 5:43

answered Dec 2, 2014 at 5:38

JLRishe

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2 Comments

Joy samvedh Over a year ago

function foo(a, b) { arguments[1] = 2; alert(arguments.length); } foo(1); why does it alert 1 and not 2. Its diff question!!!

JLRishe Over a year ago

@Joysamvedh If you have a different question, you should ask it as a different question, but the answer is that arguments is not an array, so it doesn't have all the behavior of an array.

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