index

The index of the function reference you want to mutate.

value

The value you want to mutate the reference to. This must be an exported WebAssembly function, a JavaScript wrapper for an underlying wasm function.

None (undefined).

• If index is greater than or equal to Table.prototype.length, a RangeError is thrown.
• If value is not an exported WebAssembly function or null, a TypeError is thrown.

The following example (see table2.html source code and live version) creates a new WebAssembly Table instance with an initial size of 2 references. We then print out the table length and contents of the two indexes (retrieved via Table.prototype.get()) to show that the length is two, and the indexes currently contain no function references (they currently return null).

const tbl = new WebAssembly.Table({ initial: 2, element: "anyfunc" });
console.log(tbl.length);
console.log(tbl.get(0));
console.log(tbl.get(1));

We then create an import object that contains a reference to the table:

const importObj = {
  js: { tbl },
};

Finally, we load and instantiate a wasm module (table2.wasm) using the WebAssembly.instantiateStreaming(), log the table length, and invoke the two referenced functions that are now stored in the table (the table2.wasm module (see text representation) adds two function references to the table, both of which print out a simple value):

WebAssembly.instantiateStreaming(fetch('table2.wasm'), importObject)
.then(function(obj) {
  console.log(tbl.length);
  console.log(tbl.get(0)());
  console.log(tbl.get(1)());
});

Note how you've got to include a second function invocation operator at the end of the accessor to actually invoke the referenced function and log the value stored inside it (e.g. get(0)() rather than get(0)) .

This example shows that we're creating and accessing the table from JavaScript, but the same table is visible and callable inside the wasm instance too.

• WebAssembly overview page
• WebAssembly concepts
• Using the WebAssembly JavaScript API