WebAssembly.Table.prototype.set()

The set() prototype method of the WebAssembly.Table object mutates a reference stored at a given index to a different value.

Syntax

table.set(index, value);

Parameters

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.

Return value

Void.

Exceptions

• 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.

Examples

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).

var 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:

var importObj = {
  js: {
    tbl:tbl
  }
};

Finally, we load and instantiate a wasm module (table2.wasm) using our fetchAndInstantiate() utility function, 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):

fetchAndInstantiate('table2.wasm', importObject).then(function(instance) {
  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.

Specifications

Browser compatibility

[1] WebAssembly is enabled in Firefox 52+, although disabled in the Firefox 52 Extended Support Release (ESR.)

[2] Currently supported behind the “Experimental JavaScript Features” flag. See this blog post for more details.

See also

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