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Tables

WebAssembly tables are mutable wrapper objects. A table is similar to an array, and contains function references. The contents of a table may be altered from both host code and Wasm.

Wasm tables can both be imports for, and exports from, a Wasm module or component (see the Imports section of our documentation for an example of passing imports, like a function, into a module).

Examples

Creating a Wasm table looks like this:

JavaScript
Rust, with Wasmtime

const aTableDescriptor = {
  element: "anyfunc", // anyfunc (any function) or externref (external function references)
  initial: 5, // initial number of items in the Table
  maximum: 100, // (optional) the maximum number of items the Table is allowed to contain
};

const aTable = new WebAssembly.Table(aTableDescriptor);

  let table_type = TableType::new(ValType::FuncRef, 2, None);           // declaring a table type
  let table = Table::new(&mut store, table_type, Val::FuncRef(None))?;  // creating the table

Accessing an exported table might look something like this:

JavaScript
Rust, with Wasmtime

WebAssembly.instantiateStreaming(fetch("module.wasm")).then((obj) => {
  const aTable = obj.instance.exports.tbl; // setting table reference to a variable
  const firstValue = aTable.get(0)(); // getting the first value from the table
});

let engine = Engine::default();
let mut store = Store::new(&engine, ());
let module = Module::from_file(&engine, "module.wasm")?;

let a_table = instance.get_table(&mut store, "table")
  .ok_or(anyhow::format_err!("failed to find `table` export"))?; // setting table reference to a variable

let first_value = let a_table.get(&mut store, 0);                // getting the first value from the table

Additional reading

More information about Wasm Tables can be found in Mozilla’s WebAssembly documentation.