The yaml-ast-parser npm package is a tool used for parsing YAML documents into an abstract syntax tree (AST). This allows developers to analyze and manipulate YAML data programmatically, making it useful for tasks such as configuration file processing, data validation, and transformation.

What are yaml-ast-parser's main functionalities?

Parsing YAML to AST

This feature allows the conversion of a YAML string into an AST structure. The code sample demonstrates how to parse a simple YAML text into an AST using yaml-ast-parser, which can then be traversed or manipulated according to the needs of the application.

const yamlAstParser = require('yaml-ast-parser');
const yamlText = 'a: 1\nb: 2\nc:\n  - 3\n  - 4';
const ast = yamlAstParser.load(yamlText);
console.log(ast);

Error Reporting

This feature is useful for error handling when parsing YAML. The code sample shows how to catch and report errors that occur during the parsing process, which is essential for debugging and ensuring data integrity.

const yamlAstParser = require('yaml-ast-parser');
const invalidYaml = 'a: 1\nb: \nc: 2';
try {
  yamlAstParser.load(invalidYaml);
} catch (error) {
  console.error('Parsing error:', error);
}

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Readme

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yaml-ast-parser

This is a fork of JS-YAML which supports parsing of YAML into AST.

In additional to parsing YAML to AST, it has following features:

restoration after the errors and reporting errors as a part of AST nodes.
built-in support for !include tag used in RAML

Usage

The type information below is relevant when using TypeScript, if using from JavaScript only the field/method information is relevant.

load method can be used to load the tree and returns a YAMLNode.

YAMLNode

YAMLNode class is an ancestor for all node kinds. It's kind field determine node kind, one of Kind enum:

SCALAR, MAPPING, MAP, SEQ, ANCHOR_REF or INCLUDE_REF.

After node kind is determined, it can be cast to one of the YAMLNode descendants types:

YAMLScalar, YAMLMapping, YamlMap, YAMLSequence or YAMLAnchorReference.

class	important members
`YAMLNode`	`startPosition` and `endPosition` provide node range.
`YAMLScalar`	`string` `value` field
`YAMLMapping`	`YAMLScalar` `key` and `YAMLNode` `value` fields
`YAMLSequence`	`YAMLNode[]` `items` field
`YamlMap`	`YAMLMapping[]` `mappings` field
`YAMLAnchorReference`	`string` `referencesAnchor` and `YAMLNode` `value`

YAMLScalar

Scalars are one of the three main node types defined by YAML and are effectively leaf nodes.

There are many factors that can influence the type of datum represent in scalar node (context, schema, tag, etc.).

To help inspection of a YAMLScalar to determine its datatype when a document uses the Core Schema, you can pass the YAMLScalar to the determineScalarType function. It will return an enum value indicating null, bool, int, float, or string.

Once you know the type, there are also some helper functions to help read the value by passing them the string, value: parseYamlBoolean, parseYamlFloat, and parseYamlInteger.

Keywords

FAQs

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Last updated on 04 Dec 2017

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