# Compiler
Similar to TypeScript's tsc compiling to JavaScript, AssemblyScript's asc compiles to WebAssembly.
# Command line options
# Entry file(s)
Non-option arguments are treated as the names of entry files. A single program can have multiple entries, with the exports of each entry becoming the exports of the WebAssembly module. Exports of imported files that are not entry files do not become WebAssembly module exports.
asc entryFile.ts
# General
--version, -v Prints just the compiler's version and exits.
--help, -h Prints this message and exits.
--noColors Disables terminal colors.
--config Configuration file to apply. CLI arguments take precedence.
--target Target configuration to use. Defaults to 'release'.
# asconfig.json
Instead of providing the options outlined below on the command line, a configuration file typically named asconfig.json can be used. It may look like in the following example, excluding comments:
{
"extends": "./path/to/other/asconfig.json", // (optional) base config
"entries": [
// (optional) entry files, e.g.
"./assembly/index.ts"
],
"options": {
// common options, e.g.
"importTable": true
},
"targets": {
// (optional) targets
"release": {
// additional options for the "release" target, e.g.
"optimize": true,
"binaryFile": "myModule.release.wasm"
},
"debug": {
// additional options for the "debug" target, e.g.
"debug": true,
"binaryFile": "myModule.debug.wasm"
}
}
}
Provided command line options override options in the configuration file.
# Optimization
The compiler can optimize for both speed and size. --optimizeLevel (0-3) indicates how much the compiler focuses on optimizing the code with --shrinkLevel (0-2, 1=s, 2=z) indicating how much it focuses on keeping the size low during code generation and while optimizing. A convenient shorthand is -O[optimizeLevel][shrinkLevel] , with shrink level indicated by appending the letter s (1) or z (2) to the optimize level.
--optimize, -O Optimizes the module. Typical shorthands are:
Default optimizations -O / -O3s
Make a release build -O --noAssert
Make a debug build --debug
Optimize for speed -O3
Optimize for size -O3z --converge
--optimizeLevel How much to focus on optimizing code. [0-3]
--shrinkLevel How much to focus on shrinking code size. [0-2, s=1, z=2]
--converge Re-optimizes until no further improvements can be made.
--noAssert Replaces assertions with just their value without trapping.
# Output
Typical output formats are WebAssembly binary (.wasm) and/or text format (.wat). Often, both are used in tandem to run and also inspect generated code.
--outFile, -o Specifies the output file. File extension indicates format.
--binaryFile, -b Specifies the binary output file (.wasm).
--textFile, -t Specifies the text output file (.wat).
There are several other output formats as well for tooling purposes with varying levels of maturity.
--jsFile, -j Specifies the JavaScript output file (.js).
--idlFile, -i Specifies the WebIDL output file (.webidl).
--tsdFile, -d Specifies the TypeScript definition output file (.d.ts).
# Debugging
For easier debugging a source map can be emitted alongside the WebAssembly binary.
--sourceMap Enables source map generation. Optionally takes the URL
used to reference the source map from the binary file.
It is also often useful to emit debug information, like function names, alongside the binary.
--debug Enables debug information in emitted binaries.
# Features
There are several flags that enable or disable specific WebAssembly or compiler features. By default, only the bare minimum is exposed, and fully standardized WebAssembly features will be used.
--importMemory Imports the memory from 'env.memory'.
--noExportMemory Does not export the memory as 'memory'.
--initialMemory Sets the initial memory size in pages.
--maximumMemory Sets the maximum memory size in pages.
--sharedMemory Declare memory as shared. Requires maximumMemory.
--importTable Imports the function table from 'env.table'.
--exportTable Exports the function table as 'table'.
--runtime Specifies the runtime variant to include in the program.
incremental TLSF + incremental GC (default)
minimal TLSF + lightweight GC invoked externally
stub Minimal runtime stub (never frees)
... Path to a custom runtime implementation
--exportRuntime Exports the runtime helpers (__new, __collect etc.).
--explicitStart Exports an explicit '_start' function to call.
--enable Enables WebAssembly features being disabled by default.
sign-extension Sign-extension operations
bulk-memory Bulk memory operations.
simd SIMD types and operations.
threads Threading and atomic operations.
reference-types Reference types and operations.
gc Garbage collection (anyref, WIP).
--disable Disables WebAssembly features being enabled by default.
mutable-globals Mutable global imports and exports.
--use, -u Aliases a global object under another name, e.g., to switch
the default 'Math' implementation used: --use Math=JSMath
Can also be used to introduce an integer constant.
--lowMemoryLimit Enforces very low (<64k) memory constraints.
# Linking
Specifying the base offsets of compiler-generated memory respectively the table leaves some space for other data in front. In its current form this is mostly useful to link additional data into an AssemblyScript binary after compilation, be it by populating the binary itself or initializing the data externally upon initialization. One good example is leaving some scratch space for a frame buffer.
--memoryBase Sets the start offset of emitted memory segments.
--tableBase Sets the start offset of emitted table elements.
# API
To integrate with the compiler, for example to post-process the AST, one or multiple custom transforms can be specified.
--transform Specifies the path to a custom transform to 'require'.
# Other
Other options include those forwarded to Binaryen and various flags useful in certain situations.
# Binaryen
--trapMode Sets the trap mode to use.
allow Allow trapping operations. This is the default.
clamp Replace trapping operations with clamping semantics.
js Replace trapping operations with JS semantics.
--runPasses Specifies additional Binaryen passes to run after other
optimizations, if any. See: Binaryen/src/passes/pass.cpp
--noValidate Skips validating the module using Binaryen.
# And the kitchen sink
--noColors Disables terminal colors.
--baseDir Specifies the base directory of input and output files.
--extension Specifies an alternative file extension to use.
--noUnsafe Disallows the use of unsafe features in user code.
Does not affect library files and external modules.
--noEmit Performs compilation as usual but does not emit code.
--measure Prints measuring information on I/O and compile times.
--pedantic Make yourself sad for no good reason.
--lib Adds one or multiple paths to custom library components and
uses exports of all top-level files at this path as globals.
--path Adds one or multiple paths to package resolution, similar
to node_modules. Prefers an 'ascMain' entry in a package's
package.json and falls back to an inner 'assembly/' folder.
--traceResolution Enables tracing of package resolution.
--listFiles Lists files to be compiled and exits.
-- ... Specifies node.js options (CLI only). See: node --help
# API
The compiler can also be used programmatically.