Why is "$" a valid function identifier? [duplicate]

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Possible Duplicates:

Can someone explain the dollar sign in Javascript?

Why would a javascript variable start with a dollar sign?

Why is it that I can assign a function to $ in Javascript, but not # or ^ 开发者_运维知识库?

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From the ECMA standard (Section 7.6)

The dollar sign ($) and the underscore (_) are permitted anywhere in an IdentifierName.

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Because that is what ECMA-262 specifies (see section 7.6)

Identifiers must match this RegEx: [a-zA-Z_$][0-9a-zA-Z_$]*

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The reason is because JavaScript is part of the ECMA-262 standard.

If you read section 7.6 you'll see the part about Identifier syntax.

Essentially the characters that can be used are defined by:

Identifier ::
  IdentifierName but not ReservedWord

IdentifierName ::
  IdentifierStart
  IdentifierName IdentifierPart

IdentifierStart ::
  UnicodeLetter
  $
  _
  \
  UnicodeEscapeSequence

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

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If I understand your question, it's simply because the Javascript interpreter ignores $ as any type of special character. You can assign a function to a and you can assign one to $.

Much like an underscore, it treats $ as any "normal" character.