WebAssembly in Action

D.3. Chapter 5

Chapter 5 has two exercises.

D.3.1. Exercise 1

Which keyword do you need to use to define a signature in your C or C++ code so that the compiler knows the function will be available when the code is run?

Solution

extern

D.3.2. Exercise 2

Suppose you need to include a function in Emscripten’s JavaScript code that your module will call to determine if the user’s device is online or not. How would you include a function called IsOnline that returns 1 for true and 0 (zero) for false?

Solution

In your C code, you’d define the function as shown in the following snippet:

extern int IsOnline();

When needed, your C code calls the IsOnline function as it would any other function. For example,

if (IsOnline() == 1) { /* request data ...