Extend .argument() to add default value and custom parse for command-argument

Readme.md

@@ -23,6 +23,7 @@ Read this in other languages: English | [简体中文](./Readme_zh-CN.md)
     - [Custom option processing](#custom-option-processing)
   - [Commands](#commands)
     - [Specify the argument syntax](#specify-the-argument-syntax)
+    - [Custom argument processing](#custom-argument-processing)
     - [Action handler](#action-handler)
     - [Stand-alone executable (sub)commands](#stand-alone-executable-subcommands)
   - [Automated help](#automated-help)
@@ -342,7 +343,7 @@ function myParseInt(value, dummyPrevious) {
   // parseInt takes a string and a radix
   const parsedValue = parseInt(value, 10);
   if (isNaN(parsedValue)) {
-    throw new commander.InvalidOptionArgumentError('Not a number.');
+    throw new commander.InvalidArgumentError('Not a number.');
   }
   return parsedValue;
 }
@@ -434,17 +435,19 @@ you can instead use the following method.
 
 To configure a command, you can use `.argument()` to specify each expected command-argument. 
 You supply the argument name and an optional description. The argument may be `<required>` or `[optional]`.
+You can specify a default value for an optional command-argument.
+
 
 Example file: [argument.js](./examples/argument.js)
 
 ```js
 program
   .version('0.1.0')
   .argument('<username>', 'user to login')
-  .argument('[password]', 'password for user, if required')
+  .argument('[password]', 'password for user, if required', 'no password given')
   .action((username, password) => {
     console.log('username:', username);
-    console.log('password:', password || 'no password given');
+    console.log('password:', password);
   });
 ```
 
@@ -470,6 +473,27 @@ program
   .arguments('<username> <password>');
 ```
 
+### Custom argument processing
+
+You may specify a function to do custom processing of command-arguments before they are passed to the action handler.
+The callback function receives two parameters, the user specified command-argument and the previous value for the argument.
+It returns the new value for the argument.
+
+You can optionally specify the default/starting value for the argument after the function parameter.
+
+Example file: [arguments-custom-processing.js](./examples/arguments-custom-processing.js)
+
+```js
+program
+  .command('add')
+  .argument('<first>', 'integer argument', myParseInt)
+  .argument('[second]', 'integer argument', myParseInt, 1000)
+  .action((first, second) => {
+    console.log(`${first} + ${second} = ${first + second}`);
+  })
+;
+```
+
 ### Action handler
 
 The action handler gets passed a parameter for each command-argument you declared, and two additional parameters

Readme_zh-CN.md

@@ -314,7 +314,7 @@ function myParseInt(value, dummyPrevious) {
   // parseInt takes a string and a radix
   const parsedValue = parseInt(value, 10);
   if (isNaN(parsedValue)) {
-    throw new commander.InvalidOptionArgumentError('Not a number.');
+    throw new commander.InvalidArgumentError('Not a number.');
   }
   return parsedValue;
 }
@@ -877,4 +877,4 @@ program.parse(process.argv);
 
 现在 Commander 已作为 Tidelift 订阅的一部分。
 
-Commander 和很多其他包的维护者已与 Tidelift 合作，面向企业提供开源依赖的商业支持与维护。企业可以向相关依赖包的维护者支付一定的费用，帮助企业节省时间，降低风险，改进代码运行情况。[了解更多](https://tidelift.com/subscription/pkg/npm-commander?utm_source=npm-commander&utm_medium=referral&utm_campaign=enterprise&utm_term=repo)
+Commander 和很多其他包的维护者已与 Tidelift 合作，面向企业提供开源依赖的商业支持与维护。企业可以向相关依赖包的维护者支付一定的费用，帮助企业节省时间，降低风险，改进代码运行情况。[了解更多](https://tidelift.com/subscription/pkg/npm-commander?utm_source=npm-commander&utm_medium=referral&utm_campaign=enterprise&utm_term=repo)

docs/deprecated.md

@@ -111,3 +111,32 @@ program
 
 Deprecated from Commander v8.
 
+## InvalidOptionArgumentError
+
+This was used for throwing an error from custom option processing, for a nice error message.
+
+```js
+function myParseInt(value, dummyPrevious) {
+  // parseInt takes a string and a radix
+  const parsedValue = parseInt(value, 10);
+  if (isNaN(parsedValue)) {
+    throw new commander.InvalidOptionArgumentError('Not a number.');
+  }
+  return parsedValue;
+}
+```
+
+The replacement is `InvalidArgumentError` since can be used now for custom command-argument processing too.
+
+```js
+function myParseInt(value, dummyPrevious) {
+  // parseInt takes a string and a radix
+  const parsedValue = parseInt(value, 10);
+  if (isNaN(parsedValue)) {
+    throw new commander.InvalidArgumentError('Not a number.');
+  }
+  return parsedValue;
+}
+```
+
+Deprecated from Commander v8.

esm.mjs

@@ -7,7 +7,7 @@ export const {
   createArgument,
   createOption,
   CommanderError,
-  InvalidOptionArgumentError,
+  InvalidArgumentError,
   Command,
   Argument,
   Option,

examples/argument.js

@@ -9,11 +9,11 @@ const program = new Command();
 program
   .version('0.1.0')
   .argument('<username>', 'user to login')
-  .argument('[password]', 'password for user, if required')
+  .argument('[password]', 'password for user, if required', 'no password given')
   .description('example program for argument')
   .action((username, password) => {
     console.log('username:', username);
-    console.log('password:', password || 'no password given');
+    console.log('password:', password);
   });
 
 program.parse();

examples/arguments-custom-processing.js

@@ -0,0 +1,47 @@
+#!/usr/bin/env node
+
+// This is used as an example in the README for:
+//    Custom argument processing
+//    You may specify a function to do custom processing of argument values.
+
+// const commander = require('commander'); // (normal include)
+const commander = require('../'); // include commander in git clone of commander repo
+const program = new commander.Command();
+
+function myParseInt(value, dummyPrevious) {
+  // parseInt takes a string and a radix
+  const parsedValue = parseInt(value, 10);
+  if (isNaN(parsedValue)) {
+    throw new commander.InvalidArgumentError('Not a number.');
+  }
+  return parsedValue;
+}
+
+// The previous value passed to the custom processing is used when processing variadic values.
+function mySum(value, total) {
+  return total + myParseInt(value);
+}
+
+program
+  .command('add')
+  .argument('<first>', 'integer argument', myParseInt)
+  .argument('[second]', 'integer argument', myParseInt, 1000)
+  .action((first, second) => {
+    console.log(`${first} + ${second} = ${first + second}`);
+  });
+
+program
+  .command('sum')
+  .argument('<value...>', 'values to be summed', mySum, 0)
+  .action((total) => {
+    console.log(`sum is ${total}`);
+  });
+
+program.parse();
+
+// Try the following:
+//    node arguments-custom-processing add --help
+//    node arguments-custom-processing add 2
+//    node arguments-custom-processing add 12 56
+//    node arguments-custom-processing sum 1 2 3
+//    node arguments-custom-processing sum silly

examples/options-custom-processing.js

@@ -12,7 +12,7 @@ function myParseInt(value, dummyPrevious) {
   // parseInt takes a string and a radix
   const parsedValue = parseInt(value, 10);
   if (isNaN(parsedValue)) {
-    throw new commander.InvalidOptionArgumentError('Not a number.');
+    throw new commander.InvalidArgumentError('Not a number.');
   }
   return parsedValue;
 }