Added wrapper support

The wrapper marks the unprintable characters from each style tag.
This is very useful when debugging or outputing it in different terminals. You can use it to identify the unprintable characters or even to escape them.

Also added tests for it.
Added a description about it to the readme dile.
wq

index.js

@@ -22,6 +22,10 @@ function applyOptions(obj, options) {
 	const scLevel = supportsColor ? supportsColor.level : 0;
 	obj.level = options.level === undefined ? scLevel : options.level;
 	obj.enabled = 'enabled' in options ? options.enabled : obj.level > 0;
+
+	// By default, wrappers are empty strings
+	const defaultWrapper = {pre: '', post: ''};
+	obj.wrapper = typeof options.wrapper === 'object' ? Object.assign({}, defaultWrapper, options.wrapper) : defaultWrapper;
 }
 
 function Chalk(options) {
@@ -149,6 +153,9 @@ function build(_styles, _empty, key) {
 	// See below for fix regarding invisible grey/dim combination on Windows
 	builder.hasGrey = this.hasGrey || key === 'gray' || key === 'grey';
 
+	// Setting the wrapper in case it is being used
+	builder.wrapper = this.wrapper;
+
 	// `__proto__` is used because we must return a function, but there is
 	// no way to create a function with a different prototype
 	builder.__proto__ = proto; // eslint-disable-line no-proto
@@ -189,12 +196,15 @@ function applyStyle() {
 		// Replace any instances already present with a re-opening code
 		// otherwise only the part of the string until said closing code
 		// will be colored, and the rest will simply be 'plain'.
-		str = code.open + str.replace(code.closeRe, code.open) + code.close;
+		const open = this.wrapper.pre + code.open + this.wrapper.post;
+		const close = this.wrapper.pre + code.close + this.wrapper.post;
+
+		str = open + str.replace(code.closeRe, code.open) + close;
 
 		// Close the styling before a linebreak and reopen
 		// after next line to fix a bleed issue on macOS
 		// https://github.com/chalk/chalk/pull/92
-		str = str.replace(/\r?\n/g, `${code.close}$&${code.open}`);
+		str = str.replace(/\r?\n/g, `${close}$&${open}`);
 	}
 
 	// Reset the original `dim` if we changed it to work around the Windows dimmed gray issue

readme.md

@@ -149,6 +149,26 @@ Levels are as follows:
 2. 256 color support
 3. Truecolor support (16 million colors)
 
+### chalk.wrapper
+
+The wrapper marks the unprintable characters.  
+A wrapper can be added to the styles, so you can escape characters or add marks to then.  
+By default, these wrappers are empty strings `""`.
+
+The wrappers object has two properties, `pre` and `post`.  
+For example:
+
+```js
+const ctx = new chalk.constructor({wrapper: {
+	pre: '>',
+	post: '<',
+}});
+
+ctx.red('foo') // outputs "><foo><"
+```
+
+This can be specially useful when escaping characters, using it into a _PS1_ string or debugging and outputing it into different terminals/TTYs.
+
 ### chalk.supportsColor
 
 Detect whether the terminal [supports color](https://github.com/chalk/supports-color). Used internally and handled for you, but exposed for convenience.

test/chalk.js

@@ -6,7 +6,7 @@ require('./_supports-color')(__dirname);
 const m = require('..');
 
 console.log('TERM:', process.env.TERM || '[none]');
-console.log('platform:', process.platform || '[unknown]');
+console.log('Platform:', process.platform || '[unknown]');
 
 test('don\'t add any styling when called as the base function', t => {
 	t.is(m('foo'), 'foo');

test/wrapper.js

@@ -0,0 +1,25 @@
+// Import path from 'path';
+import test from 'ava';
+// Import execa from 'execa';
+
+// Spoof supports-color
+require('./_supports-color')(__dirname);
+
+const m = require('..');
+
+m.wrapper = {
+	pre: '@',
+	post: '#'
+};
+
+test('add wrapper to underline', t => {
+	t.is(m.underline('foo'), '@\u001B[4m#foo@\u001B[24m#');
+});
+
+test('add wrapper to color', t => {
+	t.is(m.red('foo'), '@\u001B[31m#foo@\u001B[39m#');
+});
+
+test('add wrapper to bgColor', t => {
+	t.is(m.bgRed('foo'), '@\u001B[41m#foo@\u001B[49m#');
+});

types/index.d.ts

@@ -11,6 +11,12 @@ export const enum Level {
 export interface ChalkOptions {
 	enabled?: boolean;
 	level?: Level;
+	wrapper?: Wrapper;
+}
+
+export interface Wrapper {
+	pre: String,
+	post: String
 }
 
 export interface ChalkConstructor {
@@ -31,6 +37,7 @@ export interface Chalk {
 	constructor: ChalkConstructor;
 	enabled: boolean;
 	level: Level;
+	wrapper: Wrapper;
 	rgb(r: number, g: number, b: number): this;
 	hsl(h: number, s: number, l: number): this;
 	hsv(h: number, s: number, v: number): this;