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notevil

Evalulate javascript like the built-in javascript eval() method but safely.

This module uses esprima to parse the javascript AST then walks each node and evaluates the result.

Like built-in eval, the result of the last expression will be returned. Unlike built-in, there is no access to global objects, only the context that is passed in as the second object.

Built in types such as Object and String are still available, but they are wrapped so that any changes to prototypes are contained in the eval instance.

Example

var safeEval = require('notevil')
 
// basic math
var result = safeEval('1+2+3')
console.log(result) // 6
 
// context and functions
var result = safeEval('1+f(2,3)+x', {
  x: 100, 
  f: function(a,b){
    return a*b
  }
})
console.log(result) // 107
 
// multiple statements, variables and if statements
var result = safeEval('var x = 100, y = 200; if (x > y) { "cats" } else { "dogs" }')
console.log(result) // dogs
 
// inner functions
var result = safeEval('[1,2,3,4].map(function(item){ return item*100 })')
console.log(result) // [100, 200, 300, 400]

Updating context from safeEval

var context = { x: 1, obj: {y: 2} }
 
// update context global
safeEval('x = 300', context)
console.log(context.x) // 300
 
// update property on object
safeEval('obj.y = 300', context)
console.log(context.obj.y) // 300

Creating functions

var func = safeEval.Function('param', 'return param * 100')
var result = func(2)
console.log(result) // 200

Tracing errors

A .trace property is available on error objects generated by code running inside of the sandbox. It contains an array containing the esprima node stack which has a loc property, allowing you to get the line and column where the error occurred.

try {
  safeEval('throw "some error"')
} catch (ex) {
  ex.trace //=> [...esprimaAstTrace]
  ex.trace[0].loc.start.line //=> 1
}