1  ### Estraverse [![Build Status](https://secure.travis-ci.org/estools/estraverse.svg)](http://travis-ci.org/estools/estraverse)
  2  
  3  Estraverse ([estraverse](http://github.com/estools/estraverse)) is
  4  [ECMAScript](http://www.ecma-international.org/publications/standards/Ecma-262.htm)
  5  traversal functions from [esmangle project](http://github.com/estools/esmangle).
  6  
  7  ### Documentation
  8  
  9  You can find usage docs at [wiki page](https://github.com/estools/estraverse/wiki/Usage).
 10  
 11  ### Example Usage
 12  
 13  The following code will output all variables declared at the root of a file.
 14  
 15  ```javascript
 16  estraverse.traverse(ast, {
 17      enter: function (node, parent) {
 18          if (node.type == 'FunctionExpression' || node.type == 'FunctionDeclaration')
 19              return estraverse.VisitorOption.Skip;
 20      },
 21      leave: function (node, parent) {
 22          if (node.type == 'VariableDeclarator')
 23            console.log(node.id.name);
 24      }
 25  });
 26  ```
 27  
 28  We can use `this.skip`, `this.remove` and `this.break` functions instead of using Skip, Remove and Break.
 29  
 30  ```javascript
 31  estraverse.traverse(ast, {
 32      enter: function (node) {
 33          this.break();
 34      }
 35  });
 36  ```
 37  
 38  And estraverse provides `estraverse.replace` function. When returning node from `enter`/`leave`, current node is replaced with it.
 39  
 40  ```javascript
 41  result = estraverse.replace(tree, {
 42      enter: function (node) {
 43          // Replace it with replaced.
 44          if (node.type === 'Literal')
 45              return replaced;
 46      }
 47  });
 48  ```
 49  
 50  By passing `visitor.keys` mapping, we can extend estraverse traversing functionality.
 51  
 52  ```javascript
 53  // This tree contains a user-defined `TestExpression` node.
 54  var tree = {
 55      type: 'TestExpression',
 56  
 57      // This 'argument' is the property containing the other **node**.
 58      argument: {
 59          type: 'Literal',
 60          value: 20
 61      },
 62  
 63      // This 'extended' is the property not containing the other **node**.
 64      extended: true
 65  };
 66  estraverse.traverse(tree, {
 67      enter: function (node) { },
 68  
 69      // Extending the existing traversing rules.
 70      keys: {
 71          // TargetNodeName: [ 'keys', 'containing', 'the', 'other', '**node**' ]
 72          TestExpression: ['argument']
 73      }
 74  });
 75  ```
 76  
 77  By passing `visitor.fallback` option, we can control the behavior when encountering unknown nodes.
 78  
 79  ```javascript
 80  // This tree contains a user-defined `TestExpression` node.
 81  var tree = {
 82      type: 'TestExpression',
 83  
 84      // This 'argument' is the property containing the other **node**.
 85      argument: {
 86          type: 'Literal',
 87          value: 20
 88      },
 89  
 90      // This 'extended' is the property not containing the other **node**.
 91      extended: true
 92  };
 93  estraverse.traverse(tree, {
 94      enter: function (node) { },
 95  
 96      // Iterating the child **nodes** of unknown nodes.
 97      fallback: 'iteration'
 98  });
 99  ```
100  
101  When `visitor.fallback` is a function, we can determine which keys to visit on each node.
102  
103  ```javascript
104  // This tree contains a user-defined `TestExpression` node.
105  var tree = {
106      type: 'TestExpression',
107  
108      // This 'argument' is the property containing the other **node**.
109      argument: {
110          type: 'Literal',
111          value: 20
112      },
113  
114      // This 'extended' is the property not containing the other **node**.
115      extended: true
116  };
117  estraverse.traverse(tree, {
118      enter: function (node) { },
119  
120      // Skip the `argument` property of each node
121      fallback: function(node) {
122          return Object.keys(node).filter(function(key) {
123              return key !== 'argument';
124          });
125      }
126  });
127  ```
128  
129  ### License
130  
131  Copyright (C) 2012-2016 [Yusuke Suzuki](http://github.com/Constellation)
132   (twitter: [@Constellation](http://twitter.com/Constellation)) and other contributors.
133  
134  Redistribution and use in source and binary forms, with or without
135  modification, are permitted provided that the following conditions are met:
136  
137    * Redistributions of source code must retain the above copyright
138      notice, this list of conditions and the following disclaimer.
139  
140    * Redistributions in binary form must reproduce the above copyright
141      notice, this list of conditions and the following disclaimer in the
142      documentation and/or other materials provided with the distribution.
143  
144  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
145  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
146  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
147  ARE DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY
148  DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
149  (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
150  LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
151  ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
152  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
153  THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.