estraverse

What is estraverse?

The estraverse npm package is a utility for traversing and updating ECMAScript (JavaScript) abstract syntax trees (ASTs). It is commonly used in the development of JavaScript code analysis and transformation tools.

What are estraverse's main functionalities?

Traversing an AST

This feature allows you to traverse an AST, visiting all nodes in a depth-first order. You can perform actions when entering or leaving each node.

const estraverse = require('estraverse');
const ast = { /* some AST object */ };
estraverse.traverse(ast, {
  enter: function (node) {
    console.log('Entering node:', node.type);
  },
  leave: function (node) {
    console.log('Leaving node:', node.type);
  }
});

Updating an AST

This feature allows you to update nodes in an AST during traversal. In this example, it renames identifiers from 'oldName' to 'newName'.

const estraverse = require('estraverse');
const ast = { /* some AST object */ };
estraverse.replace(ast, {
  enter: function (node) {
    if (node.type === 'Identifier' && node.name === 'oldName') {
      node.name = 'newName';
      return node;
    }
  }
});

Other packages similar to estraverse

acorn

Acorn is a tiny, fast JavaScript parser that produces an AST which can be used by tools like estraverse. While Acorn focuses on parsing, estraverse focuses on traversal and modification.

babel-traverse

Babel-traverse is part of the Babel compiler ecosystem. It allows for traversing the Babel-generated AST and has more features specific to Babel's AST format, compared to estraverse which is more generic.

esquery

Esquery is a package for querying an AST using a CSS-like query syntax. It is different from estraverse in that it focuses on selecting nodes based on complex patterns rather than traversing every node.

recast

Recast provides AST traversal and transformation capabilities, similar to estraverse, but also includes pretty-printing and source map support, which estraverse does not.

README

Estraverse

Estraverse (estraverse) is ECMAScript traversal functions from esmangle project.

Documentation

You can find usage docs at wiki page.

Example Usage

The following code will output all variables declared at the root of a file.

estraverse.traverse(ast, {
    enter: function (node, parent) {
        if (node.type == 'FunctionExpression' || node.type == 'FunctionDeclaration')
            return estraverse.VisitorOption.Skip;
    },
    leave: function (node, parent) {
        if (node.type == 'VariableDeclarator')
          console.log(node.id.name);
    }
});

We can use this.skip, this.remove and this.break functions instead of using Skip, Remove and Break.

estraverse.traverse(ast, {
    enter: function (node) {
        this.break();
    }
});

And estraverse provides estraverse.replace function. When returning node from enter/leave, current node is replaced with it.

result = estraverse.replace(tree, {
    enter: function (node) {
        // Replace it with replaced.
        if (node.type === 'Literal')
            return replaced;
    }
});

By passing visitor.keys mapping, we can extend estraverse traversing functionality.

// This tree contains a user-defined `TestExpression` node.
var tree = {
    type: 'TestExpression',

    // This 'argument' is the property containing the other **node**.
    argument: {
        type: 'Literal',
        value: 20
    },

    // This 'extended' is the property not containing the other **node**.
    extended: true
};
estraverse.traverse(tree, {
    enter: function (node) { },

    // Extending the existing traversing rules.
    keys: {
        // TargetNodeName: [ 'keys', 'containing', 'the', 'other', '**node**' ]
        TestExpression: ['argument']
    }
});

By passing visitor.fallback option, we can control the behavior when encountering unknown nodes.

// This tree contains a user-defined `TestExpression` node.
var tree = {
    type: 'TestExpression',

    // This 'argument' is the property containing the other **node**.
    argument: {
        type: 'Literal',
        value: 20
    },

    // This 'extended' is the property not containing the other **node**.
    extended: true
};
estraverse.traverse(tree, {
    enter: function (node) { },

    // Iterating the child **nodes** of unknown nodes.
    fallback: 'iteration'
});

When visitor.fallback is a function, we can determine which keys to visit on each node.

// This tree contains a user-defined `TestExpression` node.
var tree = {
    type: 'TestExpression',

    // This 'argument' is the property containing the other **node**.
    argument: {
        type: 'Literal',
        value: 20
    },

    // This 'extended' is the property not containing the other **node**.
    extended: true
};
estraverse.traverse(tree, {
    enter: function (node) { },

    // Skip the `argument` property of each node
    fallback: function(node) {
        return Object.keys(node).filter(function(key) {
            return key !== 'argument';
        });
    }
});

License

Copyright (C) 2012-2016 Yusuke Suzuki (twitter: @Constellation) and other contributors.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

• Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

• Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.