Runtime
System-related functionality, process management, and observability.
function Deno.addSignalListener
addSignalListener(
signal: Signal,
handler: () => void,
): voidRegisters the given function as a listener of the given signal event.
Deno.addSignalListener(
"SIGTERM",
() => {
console.log("SIGTERM!")
}
);
Note: On Windows only "SIGINT" (CTRL+C), "SIGBREAK" (CTRL+Break), "SIGTERM", "SIGQUIT", "SIGHUP", and "SIGWINCH" are supported.
Parameters
signal: Signal handler: () => void Return Type
void function Deno.chdir
chdir(directory: string | URL): voidChange the current working directory to the specified path.
Deno.chdir("/home/userA");
Deno.chdir("../userB");
Deno.chdir("C:\\Program Files (x86)\\Java");
Throws Deno.errors.NotFound if directory not found.
Throws Deno.errors.PermissionDenied if the user does not have operating system file access rights.
Requires allow-read permission.
Parameters
directory: string | URL Return Type
void function Deno.cwd
cwd(): stringReturn a string representing the current working directory.
If the current directory can be reached via multiple paths (due to symbolic links), cwd() may return any one of them.
const currentWorkingDirectory = Deno.cwd();
Throws Deno.errors.NotFound if directory not available.
Return Type
string function Deno.execPath
execPath(): stringReturns the path to the current deno executable.
console.log(Deno.execPath()); // e.g. "/home/alice/.local/bin/deno"
Return Type
string function Deno.exit
exit(code?: number): neverExit the Deno process with optional exit code.
If no exit code is supplied then Deno will exit with return code of 0.
In worker contexts this closes the current worker using Deno's internal worker close operation. It does not call the current self.close property.
Deno.exit(5);
Parameters
code: number Return Type
never function Deno.gid
gid(): number | nullReturns the group id of the process on POSIX platforms. Returns null on windows.
console.log(Deno.gid());
Requires allow-sys permission.
Return Type
number | null function Deno.hostname
hostname(): stringGet the hostname of the machine the Deno process is running on.
console.log(Deno.hostname());
Requires allow-sys permission.
Return Type
string function Deno.loadavg
loadavg(): number[]Returns an array containing the 1, 5, and 15 minute load averages. The load average is a measure of CPU and IO utilization of the last one, five, and 15 minute periods expressed as a fractional number. Zero means there is no load. On Windows, the three values are always the same and represent the current load, not the 1, 5 and 15 minute load averages.
console.log(Deno.loadavg()); // e.g. [ 0.71, 0.44, 0.44 ]
Requires allow-sys permission.
On Windows there is no API available to retrieve this information and this method returns [ 0, 0, 0 ].
Return Type
number[] function Deno.memoryUsage
memoryUsage(): MemoryUsageReturns an object describing the memory usage of the Deno process and the V8 subsystem measured in bytes.
Return Type
function Deno.osRelease
osRelease(): stringReturns the release version of the Operating System.
console.log(Deno.osRelease());
Requires allow-sys permission. Under consideration to possibly move to Deno.build or Deno.versions and if it should depend sys-info, which may not be desirable.
Return Type
string function Deno.osUptime
osUptime(): numberReturns the Operating System uptime in number of seconds.
console.log(Deno.osUptime());
Requires allow-sys permission.
Return Type
number function Deno.refTimer
refTimer(id: number | NodeJS.Timeout): voidMake the timer of the given id block the event loop from finishing.
Parameters
id: number | NodeJS.Timeout Return Type
void function Deno.removeSignalListener
removeSignalListener(
signal: Signal,
handler: () => void,
): voidRemoves the given signal listener that has been registered with Deno.addSignalListener.
const listener = () => {
console.log("SIGTERM!")
};
Deno.addSignalListener("SIGTERM", listener);
Deno.removeSignalListener("SIGTERM", listener);
Note: On Windows only "SIGINT" (CTRL+C), "SIGBREAK" (CTRL+Break), "SIGTERM", "SIGQUIT", "SIGHUP", and "SIGWINCH" are supported.
Parameters
signal: Signal handler: () => void Return Type
void function Deno.systemMemoryInfo
systemMemoryInfo(): SystemMemoryInfoDisplays the total amount of free and used physical and swap memory in the system, as well as the buffers and caches used by the kernel.
This is similar to the free command in Linux
console.log(Deno.systemMemoryInfo());
Requires allow-sys permission.
Return Type
function Deno.uid
uid(): number | nullReturns the user id of the process on POSIX platforms. Returns null on Windows.
console.log(Deno.uid());
Requires allow-sys permission.
Return Type
number | null function Deno.unrefTimer
unrefTimer(id: number | NodeJS.Timeout): voidMake the timer of the given id not block the event loop from finishing.
Parameters
id: number | NodeJS.Timeout Return Type
void interface Deno.Env
An interface containing methods to interact with the process environment variables.
Environment variables can also be loaded from a .env file by using the --env-file flag when running a Deno program:
deno run --env-file=.env --allow-env main.ts
If --env-file is specified without a value, it defaults to loading .env from the current working directory:
deno run --env-file --allow-env main.ts
Learn more at the Deno docs.
Methods
get(key: string): string | undefined Retrieve the value of an environment variable.
Returns undefined if the supplied environment variable is not defined.
console.log(Deno.env.get("HOME")); // e.g. outputs "/home/alice"
console.log(Deno.env.get("MADE_UP_VAR")); // outputs undefined
Requires allow-env permission.
set(
key: string,
value: string,
): void Set the value of an environment variable.
Deno.env.set("SOME_VAR", "Value");
Deno.env.get("SOME_VAR"); // outputs "Value"
Requires allow-env permission.
delete(key: string): void Delete the value of an environment variable.
Deno.env.set("SOME_VAR", "Value");
Deno.env.delete("SOME_VAR"); // outputs "undefined"
Requires allow-env permission.
has(key: string): boolean Check whether an environment variable is present or not.
Deno.env.set("SOME_VAR", "Value");
Deno.env.has("SOME_VAR"); // outputs true
Requires allow-env permission.
toObject(): { [index: string]: string; } Returns a snapshot of the environment variables at invocation as a simple object of keys and values.
Deno.env.set("TEST_VAR", "A");
const myEnv = Deno.env.toObject();
console.log(myEnv.SHELL);
Deno.env.set("TEST_VAR", "B");
console.log(myEnv.TEST_VAR); // outputs "A"
Requires allow-env permission.
interface Deno.MemoryUsage
Properties
rss: number The number of bytes of the current Deno's process resident set size, which is the amount of memory occupied in main memory (RAM).
heapTotal: number The total size of the heap for V8, in bytes.
heapUsed: number The amount of the heap used for V8, in bytes.
external: number Memory, in bytes, associated with JavaScript objects outside of the JavaScript isolate.
interface Deno.SystemMemoryInfo
Information returned from a call to Deno.systemMemoryInfo.
Properties
total: number Total installed memory in bytes.
free: number Unused memory in bytes.
available: number Estimation of how much memory, in bytes, is available for starting new applications, without swapping. Unlike the data provided by the cache or free fields, this field takes into account page cache and also that not all reclaimable memory will be reclaimed due to items being in use.
buffers: number Memory used by kernel buffers.
cached: number Memory used by the page cache and slabs.
swapTotal: number Total swap memory.
swapFree: number Unused swap memory.
type alias Deno.Signal
Operating signals which can be listened for or sent to sub-processes. What signals and what their standard behaviors are OS dependent.
Definition
"SIGABRT"
| "SIGALRM"
| "SIGBREAK"
| "SIGBUS"
| "SIGCHLD"
| "SIGCONT"
| "SIGEMT"
| "SIGFPE"
| "SIGHUP"
| "SIGILL"
| "SIGINFO"
| "SIGINT"
| "SIGIO"
| "SIGPOLL"
| "SIGUNUSED"
| "SIGKILL"
| "SIGPIPE"
| "SIGPROF"
| "SIGPWR"
| "SIGQUIT"
| "SIGSEGV"
| "SIGSTKFLT"
| "SIGSTOP"
| "SIGSYS"
| "SIGTERM"
| "SIGTRAP"
| "SIGTSTP"
| "SIGTTIN"
| "SIGTTOU"
| "SIGURG"
| "SIGUSR1"
| "SIGUSR2"
| "SIGVTALRM"
| "SIGWINCH"
| "SIGXCPU"
| "SIGXFSZ"
variable Deno.args
Returns the script arguments to the program.
Give the following command line invocation of Deno:
deno eval "console.log(Deno.args)" Sushi Maguro Hamachi
Then Deno.args will contain:
[ "Sushi", "Maguro", "Hamachi" ]
If you are looking for a structured way to parse arguments, there is parseArgs() from the Deno Standard Library.
Type
string[] variable Deno.build
Information related to the build of the current Deno runtime.
Users are discouraged from code branching based on this information, as assumptions about what is available in what build environment might change over time. Developers should specifically sniff out the features they intend to use.
The intended use for the information is for logging and debugging purposes.
Properties
target: string The LLVM target triple, which is the combination of ${arch}-${vendor}-${os} and represent the specific build target that the current runtime was built for.
arch: "x86_64" | "aarch64" Instruction set architecture that the Deno CLI was built for.
os:
"darwin"
| "linux"
| "android"
| "windows"
| "freebsd"
| "netbsd"
| "aix"
| "solaris"
| "illumos"
The operating system that the Deno CLI was built for. "darwin" is also known as OSX or MacOS.
standalone: boolean vendor: string The computer vendor that the Deno CLI was built for.
env: string Optional environment flags that were set for this build of Deno CLI.
variable Deno.exitCode
The exit code for the Deno process.
If no exit code has been supplied, then Deno will assume a return code of 0.
When setting an exit code value, a number or non-NaN string must be provided, otherwise a TypeError will be thrown.
console.log(Deno.exitCode); //-> 0
Deno.exitCode = 1;
console.log(Deno.exitCode); //-> 1
Type
number variable Deno.mainModule
The URL of the entrypoint module entered from the command-line. It requires read permission to the CWD.
Also see ImportMeta for other related information.
Type
string variable Deno.noColor
Reflects the NO_COLOR environment variable at program start.
When the value is true, the Deno CLI will attempt to not send color codes to stderr or stdout and other command line programs should also attempt to respect this value.
Type
boolean variable Deno.pid
The current process ID of this instance of the Deno CLI.
console.log(Deno.pid);
Type
number variable Deno.ppid
The process ID of parent process of this instance of the Deno CLI.
console.log(Deno.ppid);
Type
number variable Deno.version
Version information related to the current Deno CLI runtime environment.
Users are discouraged from code branching based on this information, as assumptions about what is available in what build environment might change over time. Developers should specifically sniff out the features they intend to use.
The intended use for the information is for logging and debugging purposes.
Properties
deno: string Deno CLI's version. For example: "1.26.0".
v8: string The V8 version used by Deno. For example: "10.7.100.0".
V8 is the underlying JavaScript runtime platform that Deno is built on top of.
typescript: string The TypeScript version used by Deno. For example: "4.8.3".
A version of the TypeScript type checker and language server is built-in to the Deno CLI.
© 2018–2025 the Deno authors
Licensed under the MIT License.
https://docs.deno.com/api/deno/runtime
