关于\u001b转义字符
在nodejs中有这样一段代码可以使得控制台输出显示颜色，process.stderr.write('\u001b[31m error \u001b[0m :)
下面是摘自维基百科的一段内容：
The original specification only had 8 colors, and just gave them names. The SGR parameters 30-37 selected the foreground color, while 40-47 selected the background. Quite a few terminals implemented "bold" (SGR code 1) as a brighter color rather than a different font, thus providing 8 additional foreground colors. Usually you could not get these as background colors, though sometimes inverse video (SGR code 7) would allow that. Examples: to get black letters on white background use ESC[30;47m, to get red use ESC[31m, to get bright red use ESC[31;1m. To reset colors to their defaults, use ESC[39;49m (not supported on some terminals), or reset all attributes with ESC[0m.
SGR code
其中有几个关键词：ESC,SGR code, CSI codes
ESC
Unicode Character 'ESCAPE' (U+001B) 原来U+001B在unicode编码中就是被定义为转义字符 请戳这里：ESC
【备注：Unicode code points appear as U+<codepoint>】
CSI code
most of the sequences are more than two characters and start with the characters ESC and [ (left bracket/0x5B).
This sequence is called CSI for Control Sequence Introducer (or Control Sequence Initiator)
SGR code
|Code| Name| Effect|
|--|--|
|CSI n m|Select Graphic Rendition|Sets SGR parameters, including text color. After CSI can be zero or more parameters separated with; . With no parameters, CSI m is treated as CSI 0 m (reset / normal), which is typical of most of the ANSI escape sequences.|
\u001b 在不同字符集下的编码表现：
| 适用场景（不同字符集） | 编码 |
|---|---|
| HTML Entity (decimal) | � |
| HTML Entity (hex) | � |
| javascript |
\033(注意有别于8进制的utf-16) |
| C/C++/Java source code | \u001B |
| Python source code | u"\u001B"（u开头表示这是一个unicode string） |
| UTF-8 (hex) | 0x1B (1b) |
| UTF-8 (binary) | 00011011 |
| UTF-8 (octal) | 033 |
| UTF-16 (hex) | 0x001B (001b) |
| UTF-16 (decimal) | 27 |
| UTF-32 (hex) | 0x0000001B (1b) |
| UTF-32 (decimal) | 27 |
结论：
process.stderr.write('\u001b[31m error \u001b[0m)
前面的\u001b[31m用于设定SGR颜色，后面的\u001b[0m相当于一个封闭标签作为前面SGR颜色的作用范围的结束点标记。
这等价于
process.stderr.write('\033[31m error \033[0m) （注意033前面的** \ **是必须加的,这在javascript中才会被识别为八进制的33,即c++中的\u001B）
