WebAssembly.Module.customSections()
The WebAssembly.Module.customSections() static method returns a copy
of the contents of all custom sections in the given module with the given string name.
Syntax
WebAssembly.Module.customSections(module, sectionName)
Parameters
module- : The
WebAssembly.Moduleobject whose custom sections are being considered.
- : The
sectionName- : The string name of the desired custom section.
Return value
A (possibly empty) array containing {{jsxref("ArrayBuffer")}} copies of the contents of all custom sections matching sectionName.
Exceptions
If module is not a WebAssembly.Module object instance, a
{{jsxref("TypeError")}} is thrown.
Description
A Wasm module consists of a sequence of sections. Most of these sections are fully specified and validated by the Wasm spec, but modules can also contain custom sections that are ignored and skipped over during validation. (Read High level structure for information on section structures, and how normal sections (“known sections”) and custom sections are distinguished.)
This provides developers with a way to include custom data inside Wasm modules for other purposes, for example the name custom section, which allows developers to provide names for all the functions and locals in the module (like “symbols” in a native build).
Note that the WebAssembly text format currently doesn’t have a syntax specified for
adding new custom sections; you can however add a name section to your Wasm during
conversion from text format over to Wasm. The wast2wasm command available as part of
the wabt tool has a
--debug-names option — specify this during conversion to get a Wasm with a
names custom section, for example:
wast2wasm simple-name-section.was -o simple-name-section.wasm --debug-names
Examples
Using customSections
The following example uses WebAssembly.Module.customSections to check
if a loaded module instance contains a “name” custom section. A module contains a “name” custom section if WebAssembly.Module.customSections
returns an ArrayBuffer with a length greater than 0.
See custom-section.html source code and live example.
WebAssembly.compileStreaming(fetch("simple-name-section.wasm")).then((mod) => {
const nameSections = WebAssembly.Module.customSections(mod, "name");
if (nameSections.length !== 0) {
console.log("Module contains a name section");
console.log(nameSections[0]);
}
});
Specifications
{{Specifications}}
Browser compatibility
{{Compat}}