Angular CLI Prompts

Angular CLI prompts are easy to configure and improve usability and validation

Angular 7

The release of Angular 7 brought with it CLI prompts for schematics. This is nothing new for CLI’s in general but improves the user experience for Angular CLI schematics.

prettier-schematic

What’s different

Before version 7, the only way to pass schematic configuration options was to append a value or double dash key/values after the schematic like in the following examples

ng g c newComponent --selector my-new-component

This method is probably common for many developers and is used across other CLI’s. In fact, this way still works with the latest changes. If you specify an option like this with a schematic that uses prompts it will skip that prompt and use the value you supplied. +1 for backward compatibility :)

What’s new is that when executing a schematic you will now be prompted for configuration values if the developer has requested them in the collection. This is done inside the schematics schema.json file but more on that later.

What’s better

All this is to say that schematics have now become easier to use and more helpful. Easier in that you will likely not have to remember how a schematic is intended to be used as more schematics begin to leverage prompts. They can now suggest or guide you to the appropriate configuration, reducing the number of flags you have to remember or look up. A schematic can leverage the enum type and provide a list of options for the user to select.

They can also reveal new features. For example, did you know there’s a flag when ng new’ing an application, --experimental-ivy. It “Specifies whether to create a new application which uses the Ivy rendering engine.”

How to use CLI prompts

If you’re a schematic consumer there’s not much to do. First, you’ll need to upgrade your local @angular/cli to version 7.

npm i -g @angular/cli

Once the schematics you use begin leveraging this feature, you’ll see any new prompts your schematic has enabled. There are three new prompts types.

confirmation - A yes or no question; ideal for boolean options

input - textual input; ideal for string or number options

list - a predefined set of items which may be selected

If you’re a schematic author the process is almost just a simple. You’ll want to upgrade your schematic dependencies to their respective @angular version 7. Then in your schema.json file, you’ll enable a prompt for each configuration value in one of two ways, longhand, and shorthand.

Shorthand is more succinct than longhand and quite capable across all prompt types so that’s the example I’ll be discussing.

Here’s an example of a schematic configuration option from the schema.json file before converting it to a prompt.

"printWidth": {
    "type": "number",
    "description": "Specify the line length that the printer will wrap on.",
    "default": 80
}

In order to prompt the user for a selection, you can both provide suggestions and limit the possible choices with the enum type. The message displayed to the user is specified in the x-prompt field.

"printWidth": {
    "enum": [80, 100, 120, 140],
    "description": "Specify the line length that the printer will wrap on.",
    "default": 80,
    "x-prompt": "Specify the line length that the printer will wrap on (default: 80)"
}

For boolean's you likely already have type: boolean and/or a default value. To enable a prompt just add the x-prompt key and value with the prompt and you’re done. Same goes for inputs, given a ”type: string | number | integer”, add an x-prompt key/value and you’re done.

Here's an example diff migrating to CLI prompts - Github

Connecting the Schema

To make the schematic aware of the schema you'll need to configure the schema in the collection.json file. For each schematic under the schematics key, make sure you provide a schema key with a path to the appropriate schema.json file.

{
  "schematics": {
    "prettier": {
      "description": "Adds Prettier to the application.",
      "factory": "./prettier/index",
      "schema": "./prettier/schema.json"
    }
  }
}

Validation

All user responses are validated against the property's schema. For example, string type properties can use a minimum length or regular expression constraint to control the allowed values. In the event the response fails validation, the user will be asked to enter a new value.

Copy of shorthand table from the prompt docs:

Property Schema Prompt Type Notes
"type": "boolean" confirmation
"type": "string" input
"type": "number" input only valid numbers accepted
"type": "integer" input only valid numbers accepted
"enum": [...] list enum members become list selections

CLI prompt example

Here's an example of the CLI prompts from my Angular Prettier schematic.

prettier-schematic

Resources

  • schematic prompt docs
  • schema.json configuration example