CODEWITHSUNDEEP
javascriptconstructorscope
Sophie
Sophie

Reputation: 800

Undo modifications to constructor's scope on error

I have a constructor that I created which has a method which modifies a bunch of local variables. My problem is that the method may throw some error, so when an error occurs I want to restore the scope to it's previous state. Obviously I could create a bunch of temporary variables and then just assign those to the variables that the constructor actually uses, but that's not really an optimal solution. I want to know if there is any way I can modify the variables from the method and restore them to the state they were before the method was called in the case of an error.

Upvotes: 0

Views: 50

Answers (2)

sourcecode
sourcecode

Reputation: 1802

use stack,

eg.

var Stack = new Array();

doModification(10,'');

function doModification(A,B){
   Stack.push(A);
   Stack.push(B);

   // after modifying,
   try{
     A= 10; 
     if(B == 0) throw new Error("Divide by Zero Exception.");
     B= A/B;
   }
   catch(e){
     // if exception then restore original vars
     B = Stack.pop();
     A = Stack.pop();
     alert(e.description);
   }

   // else if error doesn't come then, clear the stack
   Stack = [];

}

Upvotes: 2

Brigand
Brigand

Reputation: 86270

Other than the global scope, there's no real way to interact with scopes in JavaScript. You can create objects, that act as scopes, though.

demo

function Scope(data){
  this.data = data;
  this.stages = [];
  this.save(data);
}

Scope.prototype.save = function(){
  var oldData = JSON.parse(JSON.stringify(this.data));
  this.stages.push(oldData);
}

Scope.prototype.undo = function(){
  var lastData = this.stages.pop();
  this.data = lastData;
}

We can then create a scope with some data.

var scope = new Scope({name: "John"});

Now, we have a strange function with highly preferental treatment for people named Paul.

function myFunction(data) {
  if (data.name === "John") {
    data.name = "Paul";
    throw new Error("I don't like John!");
  }
}

We can then call our function in a try/catch.

try {
  myFunction(scope.data);
}
catch (e) {
  // scope.data is {name: "Paul"}
  scope.undo();
  // scope.data is {name: "John"}
}

Upvotes: 3

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