Write WebAssembly Text Format Files(.wat) in JavaScript way.

$ npm install watjs --save

// load the module
const wat = require('./wat');

// create the module
const mod = wat.module();

// create the function $add.
const $add = wat.func('$add', {
  '0': wat.i32.as('param'),
  '1': wat.i32.as('param'),
  'lhs': wat.i32.as('local'),
  'result': wat.i32,
}, function() {
  this.get(0);
  this.get(1);
  this.f32.const(5);
  this.i32.add();
});

// export the $add as add in our module created.
mod.export('add', $add);

// output the generated .wat code
console.info(mod+'');

This library provide the following APIs to write your WAT programs.

Represents module creation, and every returned object is an instance of WATModule internally. This class provide the following methods:

import(from, name, locals) is to import some functions from JavaScript. The following example shows how to import console.log to WebAssembly runtime.

var importObject = {
  console: {
    log: function(arg) {
      console.log(arg);
    }
  }
};
fetchAndInstantiate('logger.wasm', importObject).then(function(instance) {
  instance.exports.logIt();
});

Then let's write the code in WebAssembly:

const mod = wat.module();
mod.import('console.log', '$log', {
  0: wat.i32.as('param')
});

const $logIt = wat.func('$logIt', {}, function() {
  this.i32.const(13);
  this.call('$log');
});
mod.export('logIt', logIt);

Then compile the above source code to logger.wasm, and run.

export(name, func) is to export WATFunction object in WebAssembly runtime.

• name String the name that you call at JavaScript side.
• func WATFunction your created WATFunction object which contains signature, locals and body contents.

• name String the function signature name.
• locals Object the locals object, will describe later more details.
• body Function the function to write your real instructions.

Structure your locals, the locals object is an object, which element's key represents the name of local, and the value should be an WATNumber object which could:

wat.i32
wat.i32.as('param') // (param i32)
wat.i32.as('local') // (local i32)

Write body function provides the following internal functions for inserting instructions:

• Memory/Page resizing
  • growMemory() maps to grow_memory.
  • getCurrentMemory() maps to current_memory.
• Local variables
  • get(index) maps to get_local.
  • set(index) maps to set_local.
  • tee(index) maps to tee_local.
• Global varables
  • gget(index) maps to get_global.
  • gset(index) maps to set_global.
• Control flow
  • nop() no operation, no effect.
  • block() the beginning of a block construct, a sequence of instructions with a label at the end.
  • loop() a block with a label at the beginning which may be used to form loops.
  • if() the beginning of an if construct with an implicit then block.
  • else() marks the else block of an if.
  • br() branch to a given label in an enclosing construct.
  • br_if() conditionally branch to a given label in an enclosing construct.
  • br_table() a jump table which jumps to a label in an enclosing construct.
  • return() return zero or more values from this function.
  • end() an instruction that marks the end of a block, loop, if, or function.
• Calls
  • call() maps to call.
  • call_indirect() maps to call_indirect.

And i32/i64/f32/f64 iteratly maps the following operators:

• const(val)
• load(bits, flag)
• store(bits)

i32/i64 types provides the following operators:

• add() sign-agnostic addition
• sub() sign-agnostic subtraction
• mul() sign-agnostic multiplication (lower 32-bits)
• div() division (result is truncated toward zero)
• rem() remainder (result has the sign of the dividend)
• and() sign-agnostic bitwise and
• or() sign-agnostic bitwise inclusive or
• xor() sign-agnostic bitwise exclusive or
• shl() sign-agnostic shift left
• shr() zero-replicating (logical|arithmetic) shift right
• rotl() sign-agnostic rotate left
• rotr() sign-agnostic rotate right
• eq() sign-agnostic compare equal
• ne() sign-agnostic compare unequal
• lt() less than
• le() less than or equal
• gt() greater than
• ge() greater than or equal
• clz() sign-agnostic count leading zero bits (All zero bits are considered leading if the value is zero)
• ctz() sign-agnostic count trailing zero bits (All zero bits are considered trailing if the value is zero)
• popcnt() sign-agnostic count number of one bits
• eqz() compare equal to zero (return 1 if operand is zero, 0 otherwise)

Floating point `f32/f64 operators:

• add() addition
• sub() subtraction
• mul() multiplication
• div() division
• abs() absolute value
• neg() negation
• copysign() copysign
• ceil() ceiling operator
• floor() floor operator
• trunc() round to nearest integer towards zero
• nearest() round to nearest integer, ties to even
• eq() compare ordered and equal
• ne() compare unordered or unequal
• lt() compare ordered and less than
• le() compare ordered and less than or equal
• gt() compare ordered and greater than
• ge() compare ordered and greater than or equal
• sqrt() square root
• min() minimum (binary operator); if either operand is NaN, returns NaN
• max() maximum (binary operator); if either operand is NaN, returns NaN

No license here.