October 9, 1999 - Dot Notation vs. Array Notation

Yehuda Shiran October 9, 1999
Dot Notation vs. Array Notation
Tips: October 1999

Yehuda Shiran, Ph.D.
Doc JavaScript

You can refer to properties and methods using the "dot" syntax or the array notation. In this notation, square brackets replace the dots. For example, the following example refers to a.b.d:

a["b"]["d"]

You can use the array notation for both properties and methods. The general syntax is:

objectReference["propertyName"]
objectReference["methodName"]([arguments])

It is important to understand the array notation because sometimes it is the only alternative. For example, you cannot use the dot notation when the first character of a property is a digit. When using the array notation, the name of the property must be enclosed in quotes. Here are some examples:

document["write"]("hello")
window["alert"]("howdy!")
Math["PI"]

You must use the array notation when you need to reference the name of the property through a variable. Suppose the variable str holds the string "write". Instead of document.write(), you can use:

document[str]()

However, you cannot use document.str() because it is equivalent to document["str"]().