Javascript : var 3po = true;?

Question

I read some where else that following is illegal

var 3po = true;

but

var highNoon = false;

is legal.

Could someone explain what is all this means? Why the first statement is illegal while the second is legal?

see - http://stackoverflow.com/questions/342152/why-cant-variable-names-start-with-numbers — Martijn B, Oct 24 '11 at 08:36

score 7 · Answer 1 · answered Oct 24 '11 at 08:35

An identifier cannot start with a number as the ECMAScript grammar explains:

Identifier :: 
    IdentifierName but not ReservedWord 

IdentifierName :: 
    IdentifierStart 
    IdentifierName IdentifierPart 

IdentifierStart :: 
    UnicodeLetter 
    $ 
    _ 
    \ UnicodeEscapeSequence 

IdentifierPart :: 
    IdentifierStart 
    UnicodeCombiningMark 
    UnicodeDigit 
    UnicodeConnectorPunctuation 
    <ZWNJ> 
    <ZWJ>

score 2 · Accepted Answer · answered Oct 24 '11 at 08:35

2

I think you mean legal as in Syntax-wise?

The first example will give you a SyntaxError, the reason is that variables should not begin with a number.

answered Oct 24 '11 at 08:35

MarioRicalde

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score 0 · Answer 3 · answered Oct 24 '11 at 08:41

You can find the answer in the EcmaScript documentation, page 15.

IdentifierName ::
    IdentifierStart
    IdentifierName IdentifierPart

IdentifierStart ::
    UnicodeLetter
    $
    _
    \ UnicodeEscapeSequence

So, the identifier could start from the letter, $, _ or unicode escape sequence, not the digit.

score -1 · Answer 4 · answered Oct 24 '11 at 08:44

-1

Is it possible that you meant "Why variables should not begin with a number?"

Just guesing...

answered Oct 24 '11 at 08:44

pencilCake

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Javascript : var 3po = true;?

4 Answers4