AST Tree Query

This is a very small lib for searching nodes in a javascript AST with a very simple syntax and no other dependencies.

This project was created for working on javascript AST but can also be used to work with any javascript tree-like object.

Getting Started

Install using npm :

npm install ast-tree-query

Example

const source = `
function a() {
	return 1 + 2;
}`;
const acorn = require("acorn");
const query = require("ast-tree-query");
const ast = acorn.parse(source, {ecmaVersion:2017});
console.log("Current node :", query(ast, "[.body][type=FunctionDeclaration & id.name=a][.body][.body][:first]"))
// Current node : 
// Node {
//    type: 'ReturnStatement',
//    start: 17,
//    end: 30,
//    argument:
//     Node {
//       type: 'BinaryExpression',
//       start: 24,
//       end: 29,
//       left: [Node],
//       operator: '+',
//       right: [Node] } }

Querying language

Selecting a property [.propertyName]

Get the value of a property.

// ...
const tree = {propertyName:"value"}
query(tree, "[.propertyName]"); // "value"

Selecting by index [:first] [:last] [:nth=index]

Get the first, last or nth element in the array. Similar to array[n]

// ...
const tree = ["one", ["two", "tree"]];
query(tree, "[:last][:first]"); // "two"
query(tree, "[:nth=0]"); // "one"

Filtering an array with property inside it [property=value]

Only keep elements with the property that is equal to the value. Similar to array.filter((element) => element.property === "value").

// ...
const tree = [{prop:"value1"}, {prop:"value2"}];
query(tree, "[prop=value1]"); // [{prop:"value1"}]

You can also filter for multiple properties and values with the & to join multiple filters

// ...
const tree = [{prop:"value", prop2:"value1"}, {prop:"value", prop2:"value2"}];
query(tree, "[prop=value & prop2=value1]"); // [{prop:"value", prop2:"value1"}]

You can also access a member of a property that is deeper than the current property with a .

// ...
const tree = [{prop:"value1", id:{name:"identifier"}}, {prop:"value2", id:{name:"identifier2"}}];
query(tree, "[id.name=identifier2]"); // [{prop:"value2", id:{name:"identifier2"}}]

Chaining query selectors

// ...
const tree = [{property:"property1", values:[{value:"value1"}]}, {property:"property2", values:[{value:"value2"}, {value:"value3"}]}];
query(tree, "[property=property2][.values][:last]"); // "value3"

For querying an ast:

const source = `
function a() {
	return 1 + 2;
}`;
const acorn = require("acorn");
const query = require("ast-tree-query");
const ast = acorn.parse(source, {ecmaVersion:2017});
console.log("Current node :", query(ast, "[.body][type=FunctionDeclaration & id.name=a][.body][.body][:nth=0]"))
// Current node : 
// Node {
//    type: 'ReturnStatement',
//    start: 17,
//    end: 30,
//    argument:
//     Node {
//       type: 'BinaryExpression',
//       start: 24,
//       end: 29,
//       left: [Node],
//       operator: '+',
//       right: [Node] } }