I am reading the book JavaScript: The Good Parts. It is said that
Objects in JavaScript are mutable keyed collections.
What does mutable keyed collection mean?
AS far as I could find on internet, mutable means the vales can be changes. I couldn't find what keyed collection mean.
Objects are a collection of keys with associated values. This could be referred to as a "keyed collection":
var o = {
foo: "bar",
bar: "baz"
}
(Where foo and bar here are keys).
...which can be changed (as you've already said, the "mutable" part):
o.foo = "foobar";
o.foobar = "bar";
o.foo = function() { ... }, "foo" here is the key.
Object are immutable(can not be changed) bit we do can change the values of String/Number..The keyed keyword here means that the data is "named", "indexed" or "keyed".
{
key : value,
key2: value2
}
a collection because it contains a collection of data.
It is about the way objects work in Javascript, they behave like C# Dictionaries, for example, or named arrays in PHP. obj.someKey is equivalent to obj['someKey'] and you can always change the values associated with those keys or indeed delete them.
More advanced: the key uniquely identifies the value stored with it and the system is optimized for performance, so you can use this to index information or to get distinct values of a list,etc.
