Module sections

A module is made up of several sections, some of which you'll be interacting with through the JavaScript API:

• Imports (import) are elements that can be accessed within the module and can be one of the following:
  • Function, which can be called inside the module using the call operator
  • Global, which can be accessed inside the module via the global operators
  • Linear Memory, which can be accessed inside the module via the memory operators
  • Table, which can be accessed inside the module using call_indirect
• Exports (export) are elements that can be accessed by the consuming API (that is, called by a JavaScript function)
• Module start function (start) is called after the module instance is initialized
• Global (global) contains the internal definition of global variables
• Linear memory (memory) contains the internal definition of linear memory with an initial memory size and optional maximum size
• Data (data) contains an array of data segments which specify the initial contents of fixed ranges of a given memory
• Table (table) is a linear memory whose elements are opaque values of a particular table element type:
  • In the MVP, its primary purpose is to implement indirect function calls in C/C++
• Elements (elements) is a section that allows a module to initialize the elements of any import or internally defined table with any other definition in the module
• Function and code:
  • The function section declares the signatures of each internal function defined in the module
  • The code section contains the function body of each function declared by the function section

Some of the keywords (import, export, and so on) should look familiar; they're present in the contents of the Wat file in the previous section. WebAssembly's components follow a logical mapping that directly correspond to the APIs  (for example, you pass a memory and table instance into JavaScript's WebAssembly.instantiate() function). Your primary interaction with a module in binary format will be through these APIs.