JS WebAssembly.Table

本文目录结构

WebAssembly.Table() 构造函数根据给定的大小和元素类型创建一个 Table 对象。

这是一个包装了 WebAssemble Table 的 Javascript 包装对象，具有类数组结构，存储了多个函数引用。在 Javascript 或者 WebAssemble 中创建 Table 对象可以同时被 Javascript 或 WebAssemble 访问和更改。

Syntax

var myTable = new WebAssembly.Table(tableDescriptor);

Parameters

tableDescriptor

该对象具有以下属性：

element

一个表明储存在该 Table 中对象的类型。 目前只能是： “anyfunc” （函数）。

initial

该 WebAssembly Table 初始大小。

maximum 可选

该 WebAssembly Table 允许扩展到的最大大小。

Exceptions

• 如果 tableDescriptor 不是对象类型，将会抛出 TypeError 异常。
• 如果申明了 maximum 属性并且比 initial 小，将会抛出 RangeError 异常。

Table instances

All Table instances inherit from the Table() constructor’s prototype object — this can be modified to affect all Table instances.

Instance properties

Table.prototype.constructor

Returns the function that created this object’s instance. By default this is the WebAssembly.Table() constructor.

Table.prototype.length

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

Instance methods

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.

Examples

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.

Specifications

Specification	Status	Comment
WebAssembly JavaScript Interface Table	Working Draft	Initial draft definition.