Retrieval
Values can be retrieved from an object by wrapping a string expression in a
[ ]
suffix. If the string expression is a
string literal, and if it is a legal JavaScript name and not a reserved word, then
the .
notation can be used instead. The .
notation is preferred because it is more compact and
it reads better:
stooge["first-name"] // "Jerome" flight.departure.IATA // "SYD"
The undefined
value is produced if an attempt
is made to retrieve a nonexistent member:
stooge["middle-name"] // undefined flight.status // undefined stooge["FIRST-NAME"] // undefined
The ||
operator can be used to fill in default
values:
var middle = stooge["middle-name"] || "(none)"; var status = flight.status || "unknown";
Attempting to retrieve values from undefined
will throw a TypeError
exception. This can be
guarded against with the &&
operator:
flight.equipment // undefined flight.equipment.model // throw "TypeError" flight.equipment && flight.equipment.model // undefined
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