Esvisit

Esvisit is a simple npm module for visiting JavaScript abstract syntax trees that are compatible with Mozilla parser API as described in https://developer.mozilla.org/en-US/docs/Mozilla/Projects/SpiderMonkey/Parser_API#Programs. This module supports exclusvely ECMAScript5 as described in http://www.ecma-international.org/ecma-262/5.1/. Benefits of using Esvisit includes:

• Process iteratively and avoid recursion.
• Get an alternative type that better reflects JavaScript semantic.
• Visit only actual statements and expressions.

Demonstration

var Esvisit = require('esvisit');
var Esprima = require('esprima');

function indent () { return (new Array(depth+1)).join("  ") }
function visitStatement (type, stmt) { visit('Statement', type, stmt) }
function visitExpression (type, expr) { visit('Expression', type, expr) }
function visit (kind, type, node) {
  var id = ++counter;
  console.log(indent()+'Begin'+kind+id+': '+type+'('+Esvisit.ExtractInformation(type, node).join(", ")+')')
  depth++
  push(function () {
    depth--
    console.log(indent()+'End'+id)
  })
}

var code = 'o.a = eval("2*"+x);' // Your JS code here...
var ast = Esprima.parse(code)
var counter = 0;
var depth = 0;
var push = Esvisit.Prepare(visitStatement, visitExpression)

push(ast)

Output:

BeginStatement1: Expression()
  BeginExpression2: MemberAssignment(a, =)
    BeginExpression3: EvalCall(1)
      BeginExpression4: Binary(+)
        BeginExpression5: Literal(2*)
        End5
        BeginExpression6: Identifier(x)
        End6
      End4
    End3
    BeginExpression7: Identifier(o)
    End7
  End2
End1

API

This module exposes four functions:

• Prepare(StatementCallback, ExpressionCallBack): prepare upcoming visits ; returns a function to push something on the worker list. Callbacks are called with: the Esvisit type of the current node and the current node itself. Esvisit types are described in the sections 'Statement Types' and 'Expression Types'
• ExtractInformation(EsvisitType, Node)
• ExtractStatementInformation(EsvisitType, Statement)
• ExtractExpressionInformation(EsvisitType, Expression)

Statement Types

Type | Interpretation | Information :----|:---------------|:----------- Empty | alias for EmptyStatement | [] Strict | 'use strict'; | [] Block | * | [Length] Expression | * | [] If | * | [HasAlternate] Label | * | [Label] Break | * | [MaybeLabel] Continue | * | [MaybeLabel] With | * | [] Switch | * | [Cases::[IsDefault, Length]] Return | * | [HasValue] Throw | * | [] Try | * | [BodyLength, MaybeCatchParameter, MaybeCatchLength, MaybeFinalizerLength] While | * | [] DoWhile | * | [] DeclarationFor | for (VAR_DECL; EXPR; EXPR) STMT | [Declarators::[Name, HasInit], HasTest, HasUpdate] For | for (EXPR; EXPR; EXPR) STMT | [HasInit, HasTest, HasUpdate] IdentifierForIn | for (ID in EXPR) STMT | [Name] MemberForIn | for (MEMBER in EXPR) STMT | [MaybeProperty] DeclarationForIn | for (var ID [=EXPR] in EXPR) STMT | [Name, HasInit] Definition | alias for FunctionDeclaration | [Name, Parameters::[Name], BodyLength] Declaration | alias for VariableDeclaration | [Declarators::[Name, HasInit]]

(*): Add Statement to the type to obtain the Mozilla alias.

Expression Types

Type | Interpretation | Information :----|:---------------|:----------- This | alias for ThisExpression | [] Array | ** | [Elements::[IsInitialized]] Object | ** | [Properties::[KeyValue, Kind, MaybeParameter, MaybeBodyLength]] Function | ** | [MaybeName, Parameters::[Name], BodyLength] Sequence | ** | [Length] IdentifierTypeof | typeof ID | [Name] IdentifierDelete | delete ID | [Name] MemberDelete | delete MEMBER | [MaybeProperty] Unary | ** | [Operator] Binary | ** | [Operator] IdentifierAssignment | ID ASS_OP EXPR | [Name, Operator] MemberAssignment | MEMBER ASS_OP EXPR | [MaybeProperty, Operator] IdentifierUpdate | ++ID, --ID, ID++, ID-- | [IsPrefix, Operator, Name] MemberUpdate | ++MEMBER, --MEMBER, MEMBER++, MEMBER-- | [IsPrefix, Operator, MaybeProperty] Logical | ** | [Operator] Conditional | ** | [] New | ** | [ArgumentsLength] MemberCall | MEMBER(EXPRS) | [MaybeProperty, ArgumentsLength] EvalCall | eval(EXPRS) | [ArgumentsLength] Call | EXPR(EXPRS) | [ArgumentsLength] Member | ** | [MaybeProperty] Identifier | alias for Identifier | [Name] Literal | alias for Literal | [Value]

(**): Add Expression to the type to obtain the Mozilla alias.