In Firefox console, this code will generate error:
{"d" : ["bankaccountnumber", "$1234.56"] }
> SyntaxError: invalid label {
> message="invalid label", more...}
this code works just fine
{d : ["bankaccountnumber", "$1234.56"] }
> ["bankaccountnumber", "$1234.56"]
this code works fine as well
var a = {'d' : ["bankaccountnumber", "$1234.56"] };
a.d
> ["bankaccountnumber", "$1234.56"]
Can someone help to explain why is the diference? thanks!
This is because of ambiguous syntax. When you try to make a plain object literal in the first two lines, JavaScript is really interpreting it as a set of braces, then a label, then a statement:
{
d: ["bankaccountnumber", "$1234.56"]
}
This code doesn't evaluate to an object, but just to the array. The first example, you tried to use a string as a label, which is incorrect syntax. The third example works properly, creating an object and storing it in a.
d:, the one using "d":, and the one using 'd':). Somewhat OT, but only the "d": one would be valid JSON, if that's relevant to what you're doing, because JSON is a subset of object literal notation. (json.org)
goto statements. It does have labels, which are useful for breaking out of inner loops and such. (See section 12.12 of the 5th edition specification. In earlier specs, goto was a reserved symbol but there was no goto statement -- e.g., they were hedging their bets. As of 5th edition, no more hedging.)
it is probably having a hard time deciding whether it is an expression or a block. If you use parenthesis around the object it works as it forces an expression. The grouping operator, ( and ), forces { and } to be parsed as object literal.
({"d" : ["bankaccountnumber", "$1234.56"] }) // works
Read Named function expressions demystified. Its not directly related to this issue but does address it when talking about the use of grouping-parenthesis and eval().
