Watch For File Changes And Rebuild

Watch for changes and rebuild the output JavaScript file automatically.

Terminal

bun build <path/to/entry.ts> --outfile <path/to/output.js> --watch

bun build <path/to/entry.ts> --outfile <path/to/output.js> --watch

#!/bin/bash

# Watch For File Changes And Rebuild
bun build {{path/to/entry.ts}} --outfile {{path/to/output.js}} --watch

import subprocess

# Watch For File Changes And Rebuild
# Make sure to replace <placeholders> with actual values
def run_command():
    cmd = [
        "bun",
        "build",
        "<path/to/entry.ts>",
        "--outfile",
        "<path/to/output.js>",
        "--watch"
    ]
    
    try:
        print(f"Executing: {' '.join(cmd)}")
        subprocess.run(cmd, check=True)
    except subprocess.CalledProcessError as e:
        print(f"Error: {e}")
    except FileNotFoundError:
        print("Error: bun not found. Please install it first.")

if __name__ == "__main__":
    run_command()

When To Use

During active development to ensure timely recompilation upon file modification.

Pro Tip

Use the `--verbose` flag for detailed output that can help diagnose rebuild performance issues.

Terminal Output

Expected runtime feedback

Simulated preview

Output

Watching for changes in path/to/entry.ts...

   File changed: path/to/entry.ts
   Building...

   Success! Output written to path/to/output.js
   Next build will trigger on further changes.

Anatomy of Output

Understanding the result

Bundling /path/to/entry.ts → /path/to/output.js Bundle Path

Indicates which entry file is being bundled into which output.

Watching for file changes... State

Indicates that the process is monitoring for changes.

Successfully built in 500 ms Build Time

Duration to complete the last successful build.

Troubleshooting

Common pitfalls

Error: File not found '/path/to/entry.ts'

Solution: Check the provided path for correctness.

Error: Unable to write to '/path/to/output.js'

Solution: Verify write permissions for the output directory.

Error: Build failed due to syntax error

Solution: Inspect the entry file for syntax issues.

Command Breakdown

What each part is doing

bun: Base Command; The executable that performs this operation. Here it runs Bun before the shell applies any redirect operators.
<path/to/entry.ts>: path to entry.ts; The value supplied for path to entry.ts.
<path/to/output.js>: path to output.js; The value supplied for path to output.js.
--outfile: Command Option; Tool-specific option used by this command invocation.
--watch: Command Option; Tool-specific option used by this command invocation.

How To Run

Execution path

Step 1
Run the command: `bun build path/to/entry.ts --outfile path/to/output.js --watch`
Step 2
Make a change in the 'path/to/entry.ts' file.
Step 3
Observe the rebuild process and check for the success message in the terminal.

Alternative Approaches

Comparable commands in other tools

Alternative build tools tools for the same job.

Automake / Generate Makefile In Foreign Mode automake --foreign Secon / Get Security Context Symlink Linux secon --link <path/to/symlink> Babel / Watch File For Changes And Transpile babel <path/to/input_file> --watch Dcg / Generate Code In Specific Directory dcg --directory <path/to/directory> Go / Run Go Link Tool go tool link <path/to/main.o>