Apply optional transformer to input before accepted (#642)

closes #359

README.md

@@ -113,12 +113,13 @@ A question object is a `hash` containing question related values:
 Array values can be simple `strings`, or `objects` containing a `name` (to display in list), a `value` (to save in the answers hash) and a `short` (to display after selection) properties. The choices array can also contain [a `Separator`](#separator).
 - **validate**: (Function) Receive the user input and answers hash. Should return `true` if the value is valid, and an error message (`String`) otherwise. If `false` is returned, a default error message is provided.
 - **filter**: (Function) Receive the user input and return the filtered value to be used inside the program. The value returned will be added to the _Answers_ hash.
+- **transformer**: (Function) Receive the user input and return the transformed value to be displayed to the user. The transformation only impacts what is shown while editing. It does not impact the `answers` hash.
 - **when**: (Function, Boolean) Receive the current user answers hash and should return `true` or `false` depending on whether or not this question should be asked. The value can also be a simple boolean.
 - **pageSize**: (Number) Change the number of lines that will be rendered when using `list`, `rawList`, `expand` or `checkbox`.
 - **prefix**: (String) Change the default _prefix_ message.
 - **suffix**: (String) Change the default _suffix_ message.
 
-`default`, `choices`(if defined as functions), `validate`, `filter` and `when` functions can be called asynchronous. Either return a promise or use `this.async()` to get a callback you'll call with the final value.
+`default`, `choices`(if defined as functions), `validate`, `filter` and `when` functions can be called asynchronously. Either return a promise or use `this.async()` to get a callback you'll call with the final value.
 
 ``` javascript
 {
@@ -237,7 +238,7 @@ Take `type`, `name`, `message`[, `default`] properties. `default` is expected to
 
 #### Input - `{type: 'input'}`
 
-Take `type`, `name`, `message`[, `default`, `filter`, `validate`] properties.
+Take `type`, `name`, `message`[, `default`, `filter`, `validate`, `transformer`] properties.
 
 ![Input prompt](https://cdn.rawgit.com/SBoudrias/Inquirer.js/28ae8337ba51d93e359ef4f7ee24e79b69898962/assets/screenshots/input.svg)
 

lib/prompts/input.js

@@ -41,9 +41,12 @@ class InputPrompt extends Base {
   render(error) {
     var bottomContent = '';
     var message = this.getQuestion();
+    var transformer = this.opt.transformer;
 
     if (this.status === 'answered') {
       message += chalk.cyan(this.answer);
+    } else if (transformer) {
+      message += transformer(this.rl.line);
     } else {
       message += this.rl.line;
     }

test/specs/prompts/input.js

@@ -35,4 +35,24 @@ describe('`input` prompt', function() {
       expect(this.rl.output.__raw__).to.contain('pass');
     });
   });
+
+  it('should apply the provided transform to the value', function(done) {
+    this.fixture.transformer = function(value) {
+      return value
+        .split('')
+        .reverse()
+        .join('');
+    };
+
+    var prompt = new Input(this.fixture, this.rl);
+    prompt.run();
+
+    this.rl.line = 'Inquirer';
+    this.rl.input.emit('keypress');
+
+    setTimeout(() => {
+      expect(this.rl.output.__raw__).to.contain('reriuqnI');
+      done();
+    }, 10);
+  });
 });