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esrecurse

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README.md

Esrecurse ![Build Status](https://travis-ci.org/estools/esrecurse)

Esrecurse (esrecurse) is ECMAScript recursive traversing functionality.

Example Usage

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

javascript
esrecurse.visit(ast, {
    XXXStatement: function (node) {
        this.visit(node.left);
        // do something...
        this.visit(node.right);
    }
});

We can use Visitor instance.

javascript
var visitor = new esrecurse.Visitor({
    XXXStatement: function (node) {
        this.visit(node.left);
        // do something...
        this.visit(node.right);
    }
});

visitor.visit(ast);

We can inherit Visitor instance easily.

javascript
class Derived extends esrecurse.Visitor {
    constructor()
    {
        super(null);
    }

    XXXStatement(node) {
    }
}

javascript
function DerivedVisitor() {
    esrecurse.Visitor.call(/* this for constructor */  this  /* visitor object automatically becomes this. */);
}
util.inherits(DerivedVisitor, esrecurse.Visitor);
DerivedVisitor.prototype.XXXStatement = function (node) {
    this.visit(node.left);
    // do something...
    this.visit(node.right);
};

And you can invoke default visiting operation inside custom visit operation.

javascript
function DerivedVisitor() {
    esrecurse.Visitor.call(/* this for constructor */  this  /* visitor object automatically becomes this. */);
}
util.inherits(DerivedVisitor, esrecurse.Visitor);
DerivedVisitor.prototype.XXXStatement = function (node) {
    // do something...
    this.visitChildren(node);
};

The childVisitorKeys option does customize the behaviour of this.visitChildren(node). We can use user-defined node types.

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
};
esrecurse.visit(
    ast,
    {
        Literal: function (node) {
            // do something...
        }
    },
    {
        // Extending the existing traversing rules.
        childVisitorKeys: {
            // TargetNodeName: [ 'keys', 'containing', 'the', 'other', '**node**' ]
            TestExpression: ['argument']
        }
    }
);

We can use the fallback option as well. If the fallback option is "iteration", esrecurse would visit all enumerable properties of unknown nodes. Please note circular references cause the stack overflow. AST might have circular references in additional properties for some purpose (e.g. node.parent).

javascript
esrecurse.visit(
    ast,
    {
        Literal: function (node) {
            // do something...
        }
    },
    {
        fallback: 'iteration'
    }
);

If the fallback option is a function, esrecurse calls this function to determine the enumerable properties of unknown nodes. Please note circular references cause the stack overflow. AST might have circular references in additional properties for some purpose (e.g. node.parent).

javascript
esrecurse.visit(
    ast,
    {
        Literal: function (node) {
            // do something...
        }
    },
    {
        fallback: function (node) {
            return Object.keys(node).filter(function(key) {
                return key !== 'argument'
            });
        }
    }
);

License

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 <COPYRIGHT HOLDER> 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.