@contrast/estraverse

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

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You can find usage docs at wiki page.

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

``javascript
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.

`javascript
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.

`javascript
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.

`javascript
// 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.

`javascript
// 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.

`javascript
// 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';
});
}
});
``

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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.

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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
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(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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