WATConverter

Class for converting a JavaScript AST into WebAssembly Text (WAT).

Summary

Properties

arrays	Linear-memory array allocations by variable name.
classes	Declared classes by name, each with its instance fields, per-field byte offsets, methods and total size.
currentClass	Name of the class currently being converted, if any.
currentType	Current numeric WAT type for emitted operations.
instances	Instance variable names mapped to their class names.
loopCounter	Counter for unique loop label names.
loops	Stack of enclosing loop labels used as break/continue targets.

Methods

addClassField	Adds a class field at the next available byte offset.
allocatorSource	Emits the bump allocator: a heap pointer global and an `$alloc` function.
arrayAddressSource	Computes the byte address of `baseOffset + elementIndex * 4`.
arrayIndexSource	Produces an i32 source for the element index of an array/object member access.
AssignmentExpression	Converts an AssignmentExpression node to WAT.
atDepth	Runs a function with a temporarily shifted indentation depth.
BinaryExpression	Converts a BinaryExpression node to WAT.
BlockStatement	Converts a BlockStatement node to WAT.
bodySource	Converts a loop/conditional body, accepting either a block or a single statement.
BreakStatement	Converts a BreakStatement node to WAT.
CallExpression	Converts a CallExpression node to WAT.
classConstructorSource	Converts a class constructor to a `$<Name>_new` factory that allocates a slot in the bump heap and returns the instance pointer (as f32).
ClassDeclaration	Converts a ClassDeclaration node to its factory and method functions.
classFieldAddressSource	Produces the WAT source for the heap byte address of a class field.
classFieldLoadSource	Produces the WAT source for loading a class field from the heap.
classFieldStoreSource	Produces the WAT source for storing a value into a class field.
classMethodSource	Converts a class method to a `$<Name>_<method>` function taking `$this` first.
collectConstructorFields	Collects class fields assigned in a constructor from `this.`
collectLocalNames	Collects the names of all variables declared inside a function body.
CommentBlock	Converts a CommentBlock to WAT.
CommentLine	Converts a CommentLine to WAT.
commentToSource	Converts a comment to WAT.
ConditionalExpression	Converts a ConditionalExpression (ternary) node to WAT.
ContinueStatement	Converts a ContinueStatement node to WAT.
DoWhileStatement	Converts a DoWhileStatement node to WAT.
ExportNamedDeclaration	Converts an ExportNamedDeclaration node to WAT.
ExpressionStatement	Converts an ExpressionStatement node to WAT, dropping unused values.
f32DataBytes	Serializes the f32 values of an array into raw little-endian bytes for a data segment.
ForStatement	Converts a ForStatement node to WAT.
FunctionDeclaration	Converts a FunctionDeclaration node to WAT.
getFuncNumericType	Extracts the numeric WAT type from JSDoc comments (e.
getTestSource	Produces a WAT i32 test expression for an arbitrary numeric condition.
heapStart	Computes the first unused byte, after all module-level array/object data.
Identifier	Converts an Identifier node to WAT.
IfStatement	Converts an IfStatement node to WAT.
instancePointerName	Returns the WAT local name holding an instance pointer.
isBooleanI32	Checks whether an expression already produces an i32 boolean test result, so it can be fed to `if`/`br_if` without a truthiness conversion.
isModuleDataDeclaration	Checks whether a statement is a module-level array/object constant declaration.
jsTypeToWat	Maps a JSDoc type name to a WAT numeric type.
leadingCommentsToSource	Converts leading comments to WAT.
LogicalExpression	Lowers `&&`/`\|\|` to an if/then/else that short-circuits on the left operand.
MemberExpression	Converts a MemberExpression node (array/object element read) to WAT.
NewExpression	Converts a NewExpression node to a $_new factory call.
NumericLiteral	Converts a NumericLiteral node to WAT.
percentToSource	Converts a `%` (modulo) expression, emulating float modulo via truncation.
popLoop	Removes the innermost loop from the stack.
Program	Converts a Program node to WAT.
pushLoop	Registers the current loop as innermost and returns its label names.
registerClass	Scans one class for instance fields, defaults and methods and stores its memory layout.
registerClasses	Registers top-level class declarations and their instance memory layout.
registerModuleData	Registers top-level array/object literals as flat memory data.
resolveInstanceClass	Finds the class of an instance via `this`, a tracked `new` variable, or a unique field-name match.
resolveInstanceMethodClass	Finds the class of the object a method call is dispatched on.
ReturnStatement	Converts a ReturnStatement node to WAT.
toI32	Truncates a numeric index expression to i32, passing i32 values through.
toSource	Converts a Babel AST node to WAT source.
toSource_	Dispatches a node to its handler method, emitting a warning comment for unhandled types.
trailingCommentsToSource	Converts trailing comments to WAT.
UnaryExpression	Converts an UnaryExpression node to WAT.
UpdateExpression	Converts an UpdateExpression node to WAT.
VariableDeclaration	Converts a VariableDeclaration node to WAT.
VariableDeclarator	Converts a VariableDeclarator node to WAT.
walk	Walks a Babel node tree, invoking a callback for every node.
WhileStatement	Converts a WhileStatement node to WAT.

Details

Constructor

WATConverter() #

Properties

{ [string]: {offset: number, values: number[], isObject: boolean, keys?: Map<string, number>} }arrays #

Linear-memory array allocations by variable name.

{ [string]: {fields: Array<string>, offsets: Object<string, number>, defaults: Object<string, Node>, methods: Set<string>, size: number} }classes #

Declared classes by name, each with its instance fields, per-field byte offsets, methods and total size.

string, nullcurrentClass #

Name of the class currently being converted, if any.

'f32', 'f64', 'i32', 'i64'currentType #

Current numeric WAT type for emitted operations.

{ [string]: string }instances #

Instance variable names mapped to their class names.

numberloopCounter #

Counter for unique loop label names.

{exit: string, top: string, updateSrc: string}[]loops #

Stack of enclosing loop labels used as break/continue targets.

Methods

addClassField(cls, name) #

Adds a class field at the next available byte offset.

Parameters

cls	Object	The class layout.
name	string	The field name.

allocatorSource() #

Emits the bump allocator: a heap pointer global and an $alloc function.

Parameters

Returns

string

WAT source of the heap global and allocator.

arrayAddressSource(arr, indexSrc) #

Computes the byte address of baseOffset + elementIndex * 4.

Parameters

arr	Object	The registered array/object data.
indexSrc	string	The i32 element index source.

Returns

string

WAT source that pushes the byte address.

arrayIndexSource(arr, member) #

Produces an i32 source for the element index of an array/object member access.

Parameters

arr	Object	The registered array/object data.
member	import("@babel/types").MemberExpression	The member expression.

Returns

string

WAT source that pushes the element index.

AssignmentExpression(node) #

Converts an AssignmentExpression node to WAT.

Parameters

node

import("@babel/types").AssignmentExpression

The Babel AST node.

Returns

string

WAT representation of the node.

atDepth(extra, fn) #

Runs a function with a temporarily shifted indentation depth.

Parameters

extra	number	Additional indentation depth.
fn	() => string	The function to run.

Returns

string

The result of the function.

BinaryExpression(node) #

Converts a BinaryExpression node to WAT.

Parameters

node

import("@babel/types").BinaryExpression

The Babel AST node.

Returns

string

WAT representation of the node.

BlockStatement(node) #

Converts a BlockStatement node to WAT.

Parameters

node

import("@babel/types").BlockStatement

The Babel AST node.

Returns

string

WAT representation of the node.

bodySource(body) #

Converts a loop/conditional body, accepting either a block or a single statement.

Parameters

body

Node

The body (BlockStatement or single statement).

Returns

string

WAT source of the body.

BreakStatement(node) #

Converts a BreakStatement node to WAT.

Parameters

node

import("@babel/types").BreakStatement

The Babel AST node.

Returns

string

WAT representation of the node.

CallExpression(node) #

Converts a CallExpression node to WAT.

Parameters

node

import("@babel/types").CallExpression

The Babel AST node.

Returns

string

WAT representation of the node.

classConstructorSource(node, cls) #

Converts a class constructor to a $<Name>_new factory that allocates a slot in the bump heap and returns the instance pointer (as f32).

Parameters

node	import("@babel/types").ClassDeclaration	The class declaration.
cls	Object	The registered class layout.

Returns

string

WAT source of the factory function.

ClassDeclaration(node) #

Converts a ClassDeclaration node to its factory and method functions.

Parameters

node

import("@babel/types").ClassDeclaration

The class declaration.

Returns

string

WAT representation of the class.

classFieldAddressSource(pointerName, fieldName, cls) #

Produces the WAT source for the heap byte address of a class field.

Parameters

pointerName	string	The local holding the instance pointer.
fieldName	string	The field name.
cls	Object	The class layout.

Returns

string

WAT source that pushes the byte address.

classFieldLoadSource(pointerName, fieldName, cls) #

Produces the WAT source for loading a class field from the heap.

Parameters

pointerName	string	The local holding the instance pointer.
fieldName	string	The field name.
cls	Object	The class layout.

Returns

string

WAT source that pushes the field value.

classFieldStoreSource(pointerName, valueNode, fieldName, cls) #

Produces the WAT source for storing a value into a class field.

Parameters

pointerName	string	The local holding the instance pointer.
valueNode	Node	The value expression.
fieldName	string	The field name.
cls	Object	The class layout.

Returns

string

WAT source that performs the store.

classMethodSource(clsName, method) #

Converts a class method to a $<Name>_<method> function taking $this first.

Parameters

clsName	string	The class name.
method	import("@babel/types").ClassMethod	The method definition.

Returns

string

WAT source of the method function.

collectConstructorFields(body, cls) #

Collects class fields assigned in a constructor from this.name = ... stores.

Parameters

body	import("@babel/types").BlockStatement	The constructor body.
cls	Object	The class layout.

collectLocalNames(body) #

Collects the names of all variables declared inside a function body.

Parameters

body

import("@babel/types").BlockStatement

The function body.

Returns

string[]

Names of the declared locals.

CommentBlock(node) #

Converts a CommentBlock to WAT.

Parameters

node

import("@babel/types").CommentBlock

The comment node.

Returns

string

WAT representation of the comment.

CommentLine(node) #

Converts a CommentLine to WAT.

Parameters

node

import("@babel/types").CommentLine

The comment node.

Returns

string

WAT representation of the comment.

commentToSource(comment, pos) #

Converts a comment to WAT.

Parameters

comment	import("@babel/types").Comment	The comment node.
pos	'leading', 'trailing'	The position of the comment.

Returns

string

WAT representation of the comment.

ConditionalExpression(node) #

Converts a ConditionalExpression (ternary) node to WAT.

Parameters

node

import("@babel/types").ConditionalExpression

The Babel AST node.

Returns

string

WAT representation of the node.

ContinueStatement(node) #

Converts a ContinueStatement node to WAT.

Parameters

node

import("@babel/types").ContinueStatement

The Babel AST node.

Returns

string

WAT representation of the node.

DoWhileStatement(node) #

Converts a DoWhileStatement node to WAT.

Parameters

node

import("@babel/types").DoWhileStatement

The Babel AST node.

Returns

string

WAT representation of the node.

ExportNamedDeclaration(node) #

Converts an ExportNamedDeclaration node to WAT.

Parameters

node

import("@babel/types").ExportNamedDeclaration

The Babel AST node.

Returns

string

WAT representation of the node.

ExpressionStatement(node) #

Converts an ExpressionStatement node to WAT, dropping unused values.

Parameters

node

import("@babel/types").ExpressionStatement

The Babel AST node.

Returns

string

WAT representation of the node.

f32DataBytes(values) #

Serializes the f32 values of an array into raw little-endian bytes for a data segment.

Parameters

values

number[]

The f32 values.

Returns

string

The escaped byte string.

ForStatement(node) #

Converts a ForStatement node to WAT.

Parameters

node

import("@babel/types").ForStatement

The Babel AST node.

Returns

string

WAT representation of the node.

FunctionDeclaration(node) #

Converts a FunctionDeclaration node to WAT.

Parameters

node

import("@babel/types").FunctionDeclaration

The Babel AST node.

Returns

string

WAT representation of the node.

getFuncNumericType(node) #

Extracts the numeric WAT type from JSDoc comments (e.g. @param {i32} n). Looks at the function itself and its ancestors, since Babel often attaches the comment to the wrapping ExportNamedDeclaration instead.

Parameters

node

import("@babel/types").FunctionDeclaration

The function declaration.

Returns

'f32', 'f64', 'i32', 'i64'

The numeric type.

getTestSource(expr) #

Produces a WAT i32 test expression for an arbitrary numeric condition.

Parameters

expr

Node

The condition expression.

Returns

string

WAT source that pushes an i32.

heapStart() #

Computes the first unused byte, after all module-level array/object data.

Parameters

Returns

number

The heap start offset.

Identifier(node) #

Converts an Identifier node to WAT.

Parameters

node

import("@babel/types").Identifier

The Babel AST node.

Returns

string

WAT representation of the node.

IfStatement(node) #

Converts an IfStatement node to WAT.

Parameters

node

import("@babel/types").IfStatement

The Babel AST node.

Returns

string

WAT representation of the node.

instancePointerName(objectNode) #

Returns the WAT local name holding an instance pointer.

Parameters

objectNode

Node

The object expression.

Returns

string, null

The local name.

isBooleanI32(expr) #

Checks whether an expression already produces an i32 boolean test result, so it can be fed to if/br_if without a truthiness conversion.

Parameters

expr

Node

The expression.

Returns

boolean

True if the expression yields an i32 test result.

isModuleDataDeclaration(stmt) #

Checks whether a statement is a module-level array/object constant declaration.

Parameters

stmt

import("@babel/types").Statement

The statement.

Returns

boolean

True if the statement is a module-level data declaration.

jsTypeToWat(type) #

Maps a JSDoc type name to a WAT numeric type.

Parameters

type

string

The JSDoc type name.

Returns

'f32', 'f64', 'i32', 'i64', null

The WAT type or null if not numeric.

leadingCommentsToSource(comments) #

Converts leading comments to WAT.

Parameters

comments

import("@babel/types").Comment[]

The comment nodes.

Returns

string

WAT representation of comments.

LogicalExpression(node) #

Lowers &&/|| to an if/then/else that short-circuits on the left operand.

Parameters

node

import("@babel/types").LogicalExpression

The Babel AST node.

Returns

string

WAT representation of the node.

MemberExpression(node) #

Converts a MemberExpression node (array/object element read) to WAT.

Parameters

node

import("@babel/types").MemberExpression

The Babel AST node.

Returns

string

WAT representation of the node.

NewExpression(node) #

Converts a NewExpression node to a $_new factory call.

Parameters

node

import("@babel/types").NewExpression

The Babel AST node.

Returns

string

WAT representation of the node.

NumericLiteral(node) #

Converts a NumericLiteral node to WAT.

Parameters

node

import("@babel/types").NumericLiteral

The Babel AST node.

Returns

string

WAT representation of the node.

percentToSource(node) #

Converts a % (modulo) expression, emulating float modulo via truncation.

Parameters

node

import("@babel/types").BinaryExpression

The Babel AST node.

Returns

string

WAT representation of the node.

popLoop() #

Removes the innermost loop from the stack.

Parameters

Returns

Object, undefined

The popped loop labels.

Program(node) #

Converts a Program node to WAT.

Parameters

node

import("@babel/types").Program

The Babel AST node.

Returns

string

WAT representation of the node.

pushLoop(kind, [update]) #

Registers the current loop as innermost and returns its label names.

Parameters

kind	'while', 'for', 'do'	The loop kind.
update	Node	The for-loop update expression, regenerated inline at each continue.

Returns

Object

The loop labels.

registerClass(node) #

Scans one class for instance fields, defaults and methods and stores its memory layout.

Parameters

node

import("@babel/types").ClassDeclaration

The class declaration.

registerClasses(body) #

Registers top-level class declarations and their instance memory layout.

Parameters

body

import("@babel/types").Statement[]

Top-level statements.

registerModuleData(body) #

Registers top-level array/object literals as flat memory data.

Parameters

body

import("@babel/types").Statement[]

Top-level statements.

resolveInstanceClass(objectNode, propertyName) #

Finds the class of an instance via this, a tracked new variable, or a unique field-name match.

Parameters

objectNode	Node	The member/call object expression.
propertyName	string	The accessed field or method name.

Returns

string, null

The class name.

resolveInstanceMethodClass(objectNode, methodName) #

Finds the class of the object a method call is dispatched on.

Parameters

objectNode	Node	The call object expression.
methodName	string	The called method name.

Returns

string, null

The class name.

ReturnStatement(node) #

Converts a ReturnStatement node to WAT.

Parameters

node

import("@babel/types").ReturnStatement

The Babel AST node.

Returns

string

WAT representation of the node.

toI32(expr) #

Truncates a numeric index expression to i32, passing i32 values through.

Parameters

expr

Node

The index expression.

Returns

string

WAT source that pushes an i32 index.

toSource(node) #

Converts a Babel AST node to WAT source.

Parameters

node

Node

The Babel AST node.

Returns

string

WAT representation of the node.

toSource_(node) #

Dispatches a node to its handler method, emitting a warning comment for unhandled types.

Parameters

node

Node

The Babel AST node.

Returns

string

WAT representation of the node.

trailingCommentsToSource(comments) #

Converts trailing comments to WAT.

Parameters

comments

import("@babel/types").Comment[]

The comment nodes.

Returns

string

WAT representation of comments.

UnaryExpression(node) #

Converts an UnaryExpression node to WAT.

Parameters

node

import("@babel/types").UnaryExpression

The Babel AST node.

Returns

string

WAT representation of the node.

UpdateExpression(node) #

Converts an UpdateExpression node to WAT.

Parameters

node

import("@babel/types").UpdateExpression

The Babel AST node.

Returns

string

WAT representation of the node.

VariableDeclaration(node) #

Converts a VariableDeclaration node to WAT.

Parameters

node

import("@babel/types").VariableDeclaration

The Babel AST node.

Returns

string

WAT representation of the node.

VariableDeclarator(node) #

Converts a VariableDeclarator node to WAT.

Parameters

node

import("@babel/types").VariableDeclarator

The Babel AST node.

Returns

string

WAT representation of the node.

walk(node, fn) #

Walks a Babel node tree, invoking a callback for every node.

Parameters

node	Node	The node to walk.
fn	(node: Node) => void	The callback.

WhileStatement(node) #

Converts a WhileStatement node to WAT.

Parameters

node

import("@babel/types").WhileStatement

The Babel AST node.

Returns

string

WAT representation of the node.