compact-js-ast

Synopsis

Outputs a compact string representation of the espree AST of an input program. It provides an executable compast that can be used to output
a summarized version of the AST of a given JavaScript program. The output can be in YML or JSON format. The program can be given as a file or as a string in the command line.

``
$ compast -h
Usage: compast [options] [filename]

Converts a JS program into a JSON or YML AST format

Arguments:
filename file with the original code

Options:
-V, --version output the version number
-o, --output file name of the json output program
-p, --program JS program is given in the command line
-jw --whites string ' ' Specifies the number of whites for formatting the object (default: " ")
-e --hide List of AST fields to omit (default: [])
-f --hideFile File with a line per AST fields to omit
-j --json output in JSON format (default is YML
-n --no-parse do not parse the code, assume the input is already an AST in json format
-b --babel parse the code with babel (default is espree)
-a --all output all fields
-l --location omit only location fields
-h, --help display help for command
`

Install

`
npm i -g compact-js-ast
`

Examples

Here is an example of the YML output of the AST for the program a.b(4):

`yml
$ compast -p 'a.b(4)'
type: "Program"
body:
- type: "ExpressionStatement"
expression:
type: "CallExpression"
callee:
type: "MemberExpression"
object:
type: "Identifier"
name: "a"
property:
type: "Identifier"
name: "b"
arguments:
- type: "Literal"
value: 4
`

`
$ compast -jp 'a.b(4)'
`
`json
{
"type": "Program",
"body": [
{
"type": "ExpressionStatement",
"expression": {
"type": "CallExpression",
"callee": {
"type": "MemberExpression",
"object": {
"type": "Identifier",
"name": "a"
},
"property": {
"type": "Identifier",
"name": "b"
}
},
"arguments": [
{
"type": "Literal",
"value": 4
}
]
}
}
]
}
`
Same, but removing namess and values:

`yml
$ compast -e name value -p 'a.b(4)'
type: "Program"
body:
- type: "ExpressionStatement"
expression:
type: "CallExpression"
callee:
type: "MemberExpression"
object:
type: "Identifier"
property:
type: "Identifier"
arguments:
- type: "Literal"
`

Using babel:

➜ nicolo-howto-talk git:(main) compast -blp 'a?.[0]' | yq '.program.body[0]'
`json
{
"type": "ExpressionStatement",
"expression": {
"type": "OptionalMemberExpression",
"object": {
"type": "Identifier",
"name": "a"
},
"computed": true,
"property": {
"type": "NumericLiteral",
"extra": {
"rawValue": 0,
"raw": "0"
},
"value": 0
},
"optional": true
}
}
`

See also

- astexplorer.net is a web-based tool for exploring the AST of a JavaScript program. It provides a visual representation of the AST and allows to explore the different nodes and their properties.
- jq is a lightweight and flexible command-line JSON processor. It can be used to filter and transform the output of compast to obtain a more compact representation of the AST.
- yq is a YAML version of jq
- jless is a command-line JSON viewer that can be used to visualize the output of compast` in a more readable format.