Global Functions and Variables

When running scripts with the qjs executable, several global functions and variables are automatically available without requiring module imports.

These globals are added by the qjs executable and are not available when embedding QuickJS in other applications unless explicitly configured.

Global Variables

`argv0`

string

The full path to the executable that is running the script.

console.log('Executable:', argv0);
// Output: Executable: /usr/local/bin/qjs

`scriptArgs`

string[]

Command line arguments passed to the script. The first element is always the script filename.

// Running: qjs script.js arg1 arg2
console.log(scriptArgs);
// Output: ['script.js', 'arg1', 'arg2']

`navigator.userAgent`

string

Returns a string in the format quickjs-ng/<version>.

console.log(navigator.userAgent);
// Output: quickjs-ng/0.8.0

Global Functions

`print(...args)`

Prints the arguments separated by spaces with a trailing newline.

any

Any number of arguments to print. Non-string values are converted to strings.

print('Hello', 'World', 123);
// Output: Hello World 123

`console.log(...args)`

Alias for print(). Behaves identically to print().

any

Any number of arguments to print.

console.log('Status:', 'OK');
// Output: Status: OK

Unlike browser or Node.js environments, console.log in QuickJS-ng is simply an alias for print() and does not support advanced formatting or object inspection.

`gc()`

Manually triggers garbage collection.

undefined

This function does not return a value.

// Create many temporary objects
for (let i = 0; i < 1000000; i++) {
  const obj = { value: i };
}

// Force garbage collection
gc();

When should I use gc()?

The garbage collector runs automatically when needed. Manual invocation is useful in specific scenarios:

Memory-constrained environments - Force cleanup before starting memory-intensive operations
Testing and benchmarking - Ensure consistent memory state between test runs
Long-running scripts - Periodically clean up in scripts that run for extended periods

In most cases, you should rely on automatic garbage collection.

gc() is a shorthand for std.gc() from the qjs:std module.

Comparison with Other Environments

Node.js Compatibility

QuickJS-ng globals differ from Node.js:

QuickJS-ng	Node.js	Notes
`argv0`	`process.argv[0]`	QuickJS-ng includes only the executable path
`scriptArgs`	`process.argv.slice(1)`	QuickJS-ng includes the script name
`print()`	`console.log()`	QuickJS-ng `print()` is simpler
`gc()`	`global.gc()`	Node.js requires `--expose-gc` flag

Browser Compatibility

QuickJS-ng globals differ from browsers:

QuickJS-ng	Browser	Notes
`argv0`	Not available	Browser concept doesn’t apply
`scriptArgs`	Not available	Use URL parameters in browsers
`print()`	`window.print()`	Different function entirely
`navigator.userAgent`	`navigator.userAgent`	Similar concept, different format

Example: Command-Line Script

#!/usr/bin/env qjs

if (scriptArgs.length < 2) {
  print('Usage:', scriptArgs[0], '<filename>');
  std.exit(1);
}

const filename = scriptArgs[1];
print('Processing file:', filename);

// Process file...
const content = std.loadFile(filename);
if (content === null) {
  print('Error: Could not read file');
  std.exit(1);
}

print('File size:', content.length, 'bytes');
print('User agent:', navigator.userAgent);

Next Steps

std Module

Explore the standard library module

os Module

Learn about OS-level functions

Overview

Return to stdlib overview

Overview

Core Concepts

CLI Tools

Standard Library

Advanced Topics

Platform Support

Global Functions and Variables

Global Variables

`argv0`

`scriptArgs`

`navigator.userAgent`

Global Functions

`print(...args)`

`console.log(...args)`

`gc()`

Comparison with Other Environments

Example: Command-Line Script

Next Steps

std Module

os Module

Overview

​Global Variables

​argv0

​scriptArgs

​navigator.userAgent

​Global Functions

​print(...args)

​console.log(...args)

​gc()

​Comparison with Other Environments

​Example: Command-Line Script

​Next Steps

std Module

os Module

Overview

Global Variables

`argv0`

`scriptArgs`

`navigator.userAgent`

Global Functions

`print(...args)`

`console.log(...args)`

`gc()`

Comparison with Other Environments

Example: Command-Line Script

Next Steps