Custom WASM Builds

By default, cre workflow deploy and cre workflow simulate compile your Go or TypeScript source to a WASM binary automatically — no build configuration required. This works for most workflows.

cre workflow custom-build is an opt-in feature for advanced users who need to own the build step. Once converted, the CLI delegates compilation to a Makefile in your workflow directory instead of compiling your source itself.

When to use custom WASM builds

Generally, you should consider using custom WASM builds only when you have a specific reason to take control of the compilation step. Custom workflows are particularly useful for teams that need to use a custom compiler version or toolchain that differs from the CRE default compiler.

Common reasons to use custom WASM builds:

• Custom compiler flags or build tags: Add optimization flags, conditional compilation tags, or other build-time settings not exposed by the CLI's built-in compiler
• CI/CD pipelines: Build the WASM artifact once in your pipeline and promote it across environments without recompiling
• Pre-build validation: Add linting, type checking, formatting, or security scanning steps before compilation
• Non-standard toolchains: Use a custom compiler version or toolchain that differs from the CLI default
• Language and SDK extensions: Integrate code from other languages or custom SDKs into your build pipeline

Convert a workflow to custom build

Run the following command from your project root:

cre workflow custom-build ./my-workflow

You will be prompted to confirm before any changes are made. To skip the prompt, use --force.

The following changes are made to your workflow:

• Updates workflow-path to ./wasm/workflow.wasm in your workflow.yaml for all targets
• Creates a Makefile in your workflow directory with a build target
• Creates a wasm/ output directory

Build and simulate

After conversion, install dependencies (TypeScript only), then build and simulate:

# TypeScript only
bun install

make build
cre workflow simulate ./my-workflow --target staging-settings

The CLI picks up the compiled binary at wasm/workflow.wasm automatically.

Try it yourself

Walk through the full custom build flow end to end using a hello-world project.

1. Convert your workflow to a custom build: Run the following command from your project root:

cre workflow custom-build ./my-workflow

2. Open the generated Makefile: In the my-workflow directory, you'll see a new Makefile with a build target.

Install dependencies and run the initial build:

# TypeScript only
bun install

make build
cre workflow simulate ./my-workflow --target staging-settings

For a hello-world workflow you'll see output like "Hello world!".

3. Add a custom step to your Makefile (highlighted line shows what to add):

4. Rebuild and simulate again: Run the following commands from your project root:

make build
cre workflow simulate ./my-workflow --target staging-settings

When make build runs you'll see Running my custom build step... printed before compilation.

Swap the echo for any real step: type checking, linting, code generation, or a custom compiler invocation.

Generated Makefile

The generated Makefile is ready to use. The only requirement is that make build produces wasm/workflow.wasm.

Go:

.PHONY: build

build:
	GOOS=wasip1 GOARCH=wasm CGO_ENABLED=0 go build -o wasm/workflow.wasm -trimpath -ldflags="-buildid= -w -s" .

TypeScript:

.PHONY: build

build:
	bun cre-compile main.ts wasm/workflow.wasm

Customizing the Makefile

Edit the generated Makefile to add any steps your build requires.

Example: Go with build tags:

.PHONY: build

build:
	GOOS=wasip1 GOARCH=wasm CGO_ENABLED=0 go build -tags mytag -o wasm/workflow.wasm -trimpath -ldflags="-buildid= -w -s" .

Example: TypeScript with type checking, linting, and formatting:

.PHONY: build format lint typecheck

format:
	bun run format
lint: format
	bun run lint
typecheck: lint
	bun run typecheck

build: typecheck
	bun cre-compile main.ts wasm/workflow.wasm

Learn more

• cre workflow custom-build reference: Command flags and usage
• Simulating Workflows: Testing your workflow locally
• Deploying Workflows: Deploying to the Workflow Registry