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172 lines
5.0 KiB
Markdown
172 lines
5.0 KiB
Markdown
### Esrecurse [![Build Status](https://travis-ci.org/estools/esrecurse.svg?branch=master)](https://travis-ci.org/estools/esrecurse)
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Esrecurse ([esrecurse](https://github.com/estools/esrecurse)) is
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[ECMAScript](https://www.ecma-international.org/publications/standards/Ecma-262.htm)
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recursive traversing functionality.
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### Example Usage
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The following code will output all variables declared at the root of a file.
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```javascript
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esrecurse.visit(ast, {
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XXXStatement: function (node) {
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this.visit(node.left);
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// do something...
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this.visit(node.right);
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}
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});
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```
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We can use `Visitor` instance.
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```javascript
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var visitor = new esrecurse.Visitor({
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XXXStatement: function (node) {
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this.visit(node.left);
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// do something...
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this.visit(node.right);
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}
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});
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visitor.visit(ast);
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```
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We can inherit `Visitor` instance easily.
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```javascript
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class Derived extends esrecurse.Visitor {
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constructor()
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{
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super(null);
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}
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XXXStatement(node) {
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}
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}
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```
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```javascript
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function DerivedVisitor() {
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esrecurse.Visitor.call(/* this for constructor */ this /* visitor object automatically becomes this. */);
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}
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util.inherits(DerivedVisitor, esrecurse.Visitor);
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DerivedVisitor.prototype.XXXStatement = function (node) {
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this.visit(node.left);
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// do something...
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this.visit(node.right);
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};
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```
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And you can invoke default visiting operation inside custom visit operation.
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```javascript
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function DerivedVisitor() {
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esrecurse.Visitor.call(/* this for constructor */ this /* visitor object automatically becomes this. */);
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}
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util.inherits(DerivedVisitor, esrecurse.Visitor);
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DerivedVisitor.prototype.XXXStatement = function (node) {
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// do something...
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this.visitChildren(node);
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};
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```
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The `childVisitorKeys` option does customize the behaviour of `this.visitChildren(node)`.
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We can use user-defined node types.
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```javascript
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// This tree contains a user-defined `TestExpression` node.
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var tree = {
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type: 'TestExpression',
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// This 'argument' is the property containing the other **node**.
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argument: {
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type: 'Literal',
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value: 20
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},
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// This 'extended' is the property not containing the other **node**.
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extended: true
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};
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esrecurse.visit(
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ast,
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{
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Literal: function (node) {
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// do something...
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}
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},
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{
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// Extending the existing traversing rules.
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childVisitorKeys: {
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// TargetNodeName: [ 'keys', 'containing', 'the', 'other', '**node**' ]
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TestExpression: ['argument']
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}
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}
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);
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```
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We can use the `fallback` option as well.
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If the `fallback` option is `"iteration"`, `esrecurse` would visit all enumerable properties of unknown nodes.
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Please note circular references cause the stack overflow. AST might have circular references in additional properties for some purpose (e.g. `node.parent`).
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```javascript
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esrecurse.visit(
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ast,
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{
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Literal: function (node) {
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// do something...
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}
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},
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{
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fallback: 'iteration'
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}
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);
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```
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If the `fallback` option is a function, `esrecurse` calls this function to determine the enumerable properties of unknown nodes.
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Please note circular references cause the stack overflow. AST might have circular references in additional properties for some purpose (e.g. `node.parent`).
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```javascript
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esrecurse.visit(
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ast,
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{
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Literal: function (node) {
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// do something...
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}
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},
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{
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fallback: function (node) {
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return Object.keys(node).filter(function(key) {
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return key !== 'argument'
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});
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}
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}
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);
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```
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### License
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Copyright (C) 2014 [Yusuke Suzuki](https://github.com/Constellation)
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(twitter: [@Constellation](https://twitter.com/Constellation)) and other contributors.
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions are met:
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* Redistributions of source code must retain the above copyright
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notice, this list of conditions and the following disclaimer.
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* Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in the
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documentation and/or other materials provided with the distribution.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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ARE DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY
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DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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