JavaScript: The Definitive Guide, Fourth Edition

LiveConnect Data Conversion

Java is a strongly typed language with a relatively large number of data types, while JavaScript is an untyped language with a relatively small number of types. Because of this major structural difference between the two languages, one of the central responsibilities of LiveConnect is data conversion. When JavaScript sets a Java class or instance field or passes an argument to a Java method, a JavaScript value must be converted to an equivalent Java value, and when JavaScript reads a Java class or instance field or obtains the return value of a Java method, that Java value must be converted into a compatible JavaScript value.^[77]

Figure 22-2 and Figure 22-3 illustrate how data conversion is performed when JavaScript writes Java values and when it reads them, respectively.

Figure 22-2. Data conversions performed when JavaScript writes Java values

Figure 22-3. Data conversions performed when JavaScript reads Java values

Notice the following points about the data conversions illustrated in Figure 22-2:

• Figure 22-2 does not show all possible conversions between JavaScript types and Java types. This is because JavaScript-to-JavaScript type conversions can occur before the JavaScript-to-Java conversion takes place. For example, if you pass a JavaScript number ...