mirror of https://github.com/jkjoy/sunpeiwen.git
154 lines
4.9 KiB
Markdown
154 lines
4.9 KiB
Markdown
### Estraverse [](http://travis-ci.org/estools/estraverse)
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Estraverse ([estraverse](http://github.com/estools/estraverse)) is
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[ECMAScript](http://www.ecma-international.org/publications/standards/Ecma-262.htm)
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traversal functions from [esmangle project](http://github.com/estools/esmangle).
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### Documentation
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You can find usage docs at [wiki page](https://github.com/estools/estraverse/wiki/Usage).
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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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estraverse.traverse(ast, {
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enter: function (node, parent) {
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if (node.type == 'FunctionExpression' || node.type == 'FunctionDeclaration')
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return estraverse.VisitorOption.Skip;
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},
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leave: function (node, parent) {
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if (node.type == 'VariableDeclarator')
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console.log(node.id.name);
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}
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});
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```
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We can use `this.skip`, `this.remove` and `this.break` functions instead of using Skip, Remove and Break.
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```javascript
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estraverse.traverse(ast, {
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enter: function (node) {
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this.break();
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}
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});
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```
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And estraverse provides `estraverse.replace` function. When returning node from `enter`/`leave`, current node is replaced with it.
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```javascript
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result = estraverse.replace(tree, {
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enter: function (node) {
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// Replace it with replaced.
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if (node.type === 'Literal')
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return replaced;
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}
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});
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```
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By passing `visitor.keys` mapping, we can extend estraverse traversing functionality.
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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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estraverse.traverse(tree, {
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enter: function (node) { },
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// Extending the existing traversing rules.
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keys: {
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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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By passing `visitor.fallback` option, we can control the behavior when encountering unknown nodes.
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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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estraverse.traverse(tree, {
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enter: function (node) { },
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// Iterating the child **nodes** of unknown nodes.
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fallback: 'iteration'
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});
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```
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When `visitor.fallback` is a function, we can determine which keys to visit on each node.
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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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estraverse.traverse(tree, {
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enter: function (node) { },
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// Skip the `argument` property of each node
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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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### License
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Copyright (C) 2012-2016 [Yusuke Suzuki](http://github.com/Constellation)
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(twitter: [@Constellation](http://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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