WebAssembly.Table

The WebAssembly.Table() object is a JavaScript wrapper object — an array-like structure representing a WebAssembly Table, which stores function references. A table created by JavaScript or in WebAssembly code will be accessible and mutable from both JavaScript and WebAssembly.

WebAssembly.Table()

Creates a new Table object.

Table.prototype.length

Returns the length of the table, i.e. the number of elements.

Table.prototype.get()

Accessor function — gets the element stored at a given index.

Table.prototype.grow()

Increases the size of the Table instance by a specified number of elements.

Table.prototype.set()

Sets an element stored at a given index to a given value.

The following example (see table2.html source code and live version) creates a new WebAssembly Table instance with an initial size of 2 elements. 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 both elements are null.

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

We then create an import object that contains the table:

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

Finally, we load and instantiate a wasm module (table2.wasm) using the WebAssembly.instantiateStreaming() method. The table2.wasm module contains two functions (one that returns 42 and another that returns 83) and stores both into elements 0 and 1 of the imported table (see text representation). So after instantiation, the table still has length 2, but the elements now contain callable Exported WebAssembly Functions which we can call from JS.

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