javascript

Chapter 5: Reference Types
literals have become a preferred way of passing a large number of optional arguments to a function, such
as in this example:
function displayInfo(args) {
var output = “”;
if (typeof args.name == “string”){
output += “Name: “ + args.name + “\n”;
}
if (typeof args.age == “number”) {
output += “Age: “ + args.age + “\n”;
}
}
alert(output);
displayInfo({
name: “Nicholas”,
age: 29
});
displayInfo({
name: “Greg”
});
Here, the function displayInfo() accepts a single argument named args . The argument may come in
with a property called name or age , or both or neither of those. The function is set up to test for the
existence of each property using the typeof operator and then to construct a message to display based
on their availability. This function is then called twice, each time with different data specified in an object
literal. The function works correctly in both cases.
This pattern for argument passing is best used when there is a large number of optional arguments that
can be passed into the function. Generally speaking, named arguments are easier to work with but can
get unwieldy when there are numerous optional arguments. The best approach is to use named
arguments for those that are required, and an object literal to encompass multiple optional arguments.
Although object properties are typically accessed using dot notation, which is common to many object -
oriented languages, it ’ s also possible to access properties via bracket notation. When you use bracket
notation, a string containing the property name is placed between the brackets, as in this example:
alert(person[“name”]);
alert(person.name);
//”Nicholas”
//”Nicholas”
Functionally, there is no difference between the two approaches. The main advantage of bracket notation
is that it allows you to use variables for property access, such as in this example:
var propertyName = “name”;
alert(person[propertyName]);
//”Nicholas”
Generally speaking, dot notation is preferred unless variables are necessary to access properties
by name.
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