src: add config file support · nodejs/node@9fd217d

your application behaviour is unaffected by this change before using it in

production.

### `--experimental-config-file`

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added: REPLACEME

-->

> Stability: 1.0 - Early development

Use this flag to specify a configuration file that will be loaded and parsed

before the application starts.

Node.js will read the configuration file and apply the settings.

The configuration file should be a JSON file

with the following structure:

```json

{

"$schema": "https://nodejs.org/dist/REPLACEME/docs/node_config_json_schema.json",

"experimental-transform-types": true,

"import": [

"amaro/transform"

],

"disable-warning": "ExperimentalWarning",

"watch-path": "src",

"watch-preserve-output": true

}

```

Only flags that are allowed in [`NODE_OPTIONS`][] are supported.

No-op flags are not supported.

Not all V8 flags are currently supported.

It is possible to use the [official JSON schema](../node_config_json_schema.json)

to validate the configuration file, which may vary depending on the Node.js version.

Each key in the configuration file corresponds to a flag that can be passed

as a command-line argument. The value of the key is the value that would be

passed to the flag.

For example, the configuration file above is equivalent to

the following command-line arguments:

```bash

node --experimental-transform-types --import amaro/transform --disable-warning=ExperimentalWarning --watch-path=src --watch-preserve-output

```

The priority in configuration is as follows:

1. NODE\_OPTIONS and command-line options

2. Configuration file

3. Dotenv NODE\_OPTIONS

Values in the configuration file will not override the values in the environment

variables and command-line options, but will override the values in the `NODE_OPTIONS`

env file parsed by the `--env-file` flag.

If duplicate keys are present in the configuration file, only

the first key will be used.

The configuration parser will throw an error if the configuration file contains

unknown keys or keys that cannot used in `NODE_OPTIONS`.

Node.js will not sanitize or perform validation on the user-provided configuration,

so **NEVER** use untrusted configuration files.

### `--experimental-eventsource`

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