estraverse

ECMAScript JS AST traversal functions

Estraverse

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

You can find usage docs at wiki page.

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

estraverse.traverse(ast, {
    enterfunction (nodeparent) {
        if (node.type == 'FunctionExpression' || node.type == 'FunctionDeclaration')
            return estraverse.VisitorOption.Skip;
    },
    leavefunction (nodeparent) {
        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.

estraverse.traverse(ast, {
    enterfunction (node) {
        this.break();
    }
});

And estraverse provides estraverse.replace function. When returning node from enter/leave, current node is replaced with it.

result = estraverse.replace(tree, {
    enterfunction (node) {
        // Replace it with replaced. 
        if (node.type === 'Literal')
            return replaced;
    }
});

By passing visitor.keys mapping, we can extend estraverse traversing functionality.

// 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, {
    enterfunction (node) { },
 
    // Extending the exising 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.

// 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, {
    enterfunction (node) { },
 
    // Iterating the child **nodes** of unknown nodes. 
    fallback: 'iteration'
});

Copyright (C) 2012-2013 Yusuke Suzuki (twitter: @Constellation) and other contributors.

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