Esrecurse

Esrecurse (esrecurse) is
ECMAScript
recursive traversing functionality.

Example Usage

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

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

We can use Visitor instance.

 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.

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

    XXXStatement(node) {
    }
}

 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.

 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.

 // 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).

 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).

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

License

Copyright (C) 2014 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.

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 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.