Pass values from command line, environment and CLI config to code when build\serve

[Flybbit]

Requirement
I have three app in project. They use shared code. AppA uses part A from shared code, AppB uses part B and third AppC uses both A and B parts. So I need something like conditional compilation to reduce bundle size for AppA and AppB.
Another requirement is to pass some parameters like connection address or build number to code.
Third one feature which could be nice to have is ability to define environment variable on computer and use it when build\serve. So on dev machine you can get only dev build - "safety barrier".

Possible solution
Webpack has DefinePlugin and it can help to implement all three features. We should just change CLI config schema

"defines": {
  "type": "array",
  "description": "defines",
  "items": {                             
        "type": "object",
        "properties": {
          "name": {
            "type": "string",
            "description": "Name of the def"
          },
          "value": {
            "oneOf": [{"type": "string"}, {"type": "number"}, {"type": "boolean"}],
            "description": "Value of the def for all targets"
          },
           "targets": {
            "type": "object",
            "properties": {
              "development": {
                "oneOf": [{"type": "string"}, {"type": "number"}, {"type": "boolean"}],
                "description": "Value of the def for development target"
              },
              "production": {
                "oneOf": [{"type": "string"}, {"type": "number"}, {"type": "boolean"}],
                "description": "Value of the def for production target"
              }
            }
          }
        }
  },
  "default": []
}

and add plugin in common webpack config

new webpack.DefinePlugin(
  appConfig.defines.reduce(
    (defines, item) => {
      if (item && item.name){
        let name = item.name;
        let value = item.targets ? item.targets[buildOptions.target] : item.value;
        if (typeof value === 'string') {
          value = JSON.stringify(eval(value));                      
        }
        defines[name] = value;
      }                  
      return defines;
    }, {}
  )
)

How to use:

1. config your app

  "defines": [
    {
      "name": "DEFINE_OPTION",
      "value": true
    },
    {
      "name": "ENV_OPTION",
      "value": "process.env.ENV_OPTION"
    },
    {
      "name": "COMMAND_LINE_OPTION",
      "value": "buildOptions.command_line_option"
    },
    {
      "name": "CALC_OPTION",
      "value": "2 + 2"
    }
  ]

2. Run

ENV_OPTION="my value"
ng serve --command_line_option=42

somewhere in your code

declare var DEFINE_OPTION: boolean;
declare var ENV_OPTION: string;
declare var COMMAND_LINE_OPTION: string;
declare var CALC_OPTION: number;


if (DEFINE_OPTION){
  //this code will be excluded by optimizer if !DEFINE_OPTION  
}

As bonus (?) you can define some logic (see CALC_OPTION). Another thing - access to buildOptions. It allows to get command line args fast and easy, but looks a bit dirty

[filipesilva]

Hi there, this functionality is something we have considered before and opted to not include in Angular CLI. I know doing what you propose is common in webpack projects but this isn't the approach we want to follow in Angular CLI.

Generally speaking, the use case you mentioned (different code in different builds), is addressed by our file replacement functionality (https://github.com/angular/angular-cli/wiki/stories-application-environments).

[Flybbit]

@filipesilva Thanks, replacement really solves half of problem. What could you advice for second half: pass environment\command line to code. I found Issue #4419. According to comments there solution is to generate ts code before build. Is it right approach at the moment?

[filipesilva]

I don't see us passing generic values from the CLI to the files anytime soon. The approach we suggest is to have that code on disk and replace it according to needs.

You can also use the
ng serve --args "var1=varValue1,var2=varValue2"

Then write a "command line arguments string parser" that just dumps all of those into
process.env

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