Programming will inevitably write the configuration file, how to write the configuration is also a science.
YAML is designed to write the language configuration file, it is very simple and powerful and convenient than the JSON format.
This article describes the YAML syntax to JS-YAML implementation example. You can go online Demo verify the following example.
I. Introduction
YAML language (pronunciation / jæməl /) design goal is to facilitate human reader. It is essentially a common serial data format.
Its basic syntax rules are as follows.
- Case Sensitive
- Use indention hierarchy
- Not allowed to use the Tab key to indent only allows the use of space.
- The number of spaces to indent does not matter, as long as the left elements are aligned to the same level
# Indicates a comment from this character until the end of the line, the parser will be ignored.
YAML data structure supported by three.
- Object: a set of keys, also known as mapping (mapping) / hashes (hashes) / Dictionary (dictionary)
- Array: a set of values are arranged in order, also known sequence (sequence) / list (list)
- Scalar (scalars): individual, can not be divided value
The following sections describe these three data structures.
Second, the object
A set of key-value object of using the structure represented by colons.
animal: pets
JavaScript turned follows.
{ animal: 'pets' }
Yaml also allows another way, all the key-value pairs within the object written as a row.
hash: { name: Steve, foo: bar }
JavaScript turned follows.
{ hash: { name: 'Steve', foo: 'bar' } }
Third, the array
A set of row lines beginning conjunction form an array.
- Cat - Dog - Goldfish
JavaScript turned follows.
[ 'Cat', 'Dog', 'Goldfish' ]
Child members of the data structure is an array, it can be indented one space in the below.
- - Cat - Dog - Goldfish
JavaScript turned follows.
[ [ 'Cat', 'Dog', 'Goldfish' ] ]
Array notation may be employed within the row.
animal: [Cat, Dog]
JavaScript turned follows.
{ animal: [ 'Cat', 'Dog' ] }
Fourth, the composite structure
And using the array of objects may be combined to form a composite structure.
languages: - Ruby - Perl - Python websites: YAML: yaml.org Ruby: ruby-lang.org Python: python.org Perl: use.perl.org
JavaScript turned follows.
{ languages: [ 'Ruby', 'Perl', 'Python' ], websites: { YAML: 'yaml.org', Ruby: 'ruby-lang.org', Python: 'python.org', Perl: 'use.perl.org' } }
V. scalar
Scalar is the most basic, the value can not be divided. The following data types are all pure amount of JavaScript.
- String
- Boolean value
- Integer
- Float
- Null
- time
- date
Values are expressed directly as literals.
number: 12.30
JavaScript turned follows.
{ number: 12.30 }
Boolean value trueand falserepresent.
isSet: true
JavaScript turned follows.
{ isSet: true }
nullWith ~representation.
parent: ~
JavaScript turned follows.
{ parent: null }
Time in ISO8601 format.
iso8601: 2001-12-14t21:59:43.10-05:00
JavaScript turned follows.
{ iso8601: new Date('2001-12-14t21:59:43.10-05:00') }
Date composite iso8601 format year, month, day.
date: 1976-07-31
JavaScript turned follows.
{ date: new Date('1976-07-31') }
YAML allows two exclamation points, cast data types.
e: !!str 123 f: !!str true
JavaScript turned follows.
{ e: '123', f: 'true' }
Six String
String is the most common, and most complex data type.
String Default does not use quotation marks.
str: 这是一行字符串
JavaScript turned follows.
{ str: '这是一行字符串' }
If among the string contains spaces or special characters, you need to be placed in quotation marks.
str: '内容： 字符串'
JavaScript turned follows.
{ str: '内容: 字符串' }
Single and double quotes can be used, double quotes will not escape special characters.
s1: '内容\n字符串' s2: "内容\n字符串"
JavaScript turned follows.
{ s1: '内容\\n字符串', s2: '内容\n字符串' }
Among the single quotation marks if there is a single quote, you must use two single quotes to escape.
str: 'labor''s day'
JavaScript turned follows.
{ str: 'labor\'s day' }
String can be written in multiple lines start from the second row, there must be a single space indent. Line breaks will be converted to spaces.
str: 这是一段 多行 字符串
JavaScript turned follows.
{ str: '这是一段 多行 字符串' }
Multiline strings may be used |to retain line breaks, it can also be used >folded wrap.
this: | Foo Bar that: > Foo Bar
Into JavaScript code is as follows.
{ this: 'Foo\nBar\n', that: 'Foo Bar\n' }
+Represents a block of text at the end of the reserved line breaks, -it represents the end of the string deleted wrap.
s1: | Foo s2: |+ Foo s3: |- Foo
Into JavaScript code is as follows.
{ s1: 'Foo\n', s2: 'Foo\n\n\n', s3: 'Foo' }
HTML tags can be inserted into the string.
message: | <p style="color: red"> 段落 </p>
JavaScript turned follows.
{ message: '\n<p style="color: red">\n 段落\n</p>\n' }
Seven references
Anchors &and aliases *can be used to reference.
defaults: &defaults adapter: postgres host: localhost development: database: myapp_development <<: *defaults test: database: myapp_test <<: *defaults
It is equivalent to the following code.
defaults: adapter: postgres host: localhost development: database: myapp_development adapter: postgres host: localhost test: database: myapp_test adapter: postgres host: localhost
&Used to create an anchor point ( defaults), <<represents the merged into the current data, *is used to reference anchor.
Here is another example.
- &showell Steve - Clark - Brian - Oren - *showell
Into JavaScript code is as follows.
[ 'Steve', 'Clark', 'Brian', 'Oren', 'Steve' ]
Eight, the regular expression functions and conversion
This is the JS-YAML Kut some features, functions, and can be a regular expression to a string.
# example.yml fn: function () { return 1 } reg: /test/
Yml code analysis above document is as follows.
var yaml = require('js-yaml'); var fs = require('fs'); try { var doc = yaml.load( fs.readFileSync('./example.yml', 'utf8') ); console.log(doc); } catch (e) { console.log(e); }
JavaScript objects restored from the code yaml file is as follows.
var yaml = require('js-yaml'); var fs = require('fs'); var obj = { fn: function () { return 1 }, reg: /test/ }; try { fs.writeFileSync( './example.yml', yaml.dump(obj), 'utf8' ); } catch (e) { console.log(e); }