WebAssembly.Table()

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。

Note: Tables 对象目前只能存储函数引用,不过在将来可能会被扩展。

语法

var myTable = new WebAssembly.Table(tableDescriptor);

参数

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。

异常

  • 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 Instance

所有Table实例都继承自Table()构造函数的原型对象-可以对其进行修改以影响所有Table实例。

Instance 属性

Table.prototype.constructor
返回创建该对象实例的函数。默认情况下,这是WebAssembly.Table()构造函数。
Table.prototype.length
返回Table的长度,即元素数。

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.

例子

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.

规范

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

浏览器兼容性

BCD tables only load in the browser

相关链接