在JavaScript中创建和为动态全局变量赋值

Question

I have a requirement in my JavaScript code where I update a global variables dynamically to take a particular action based on the value of those variables.

Eg :

this.decEnabled + this.properties.itemIndex = false;  

Here, "this.properties.itemIndex" is integer that helps to distinguish between the items & this.decEnabled is a global variable i am trying to create. But I get an error : Uncaught exception: ReferenceError: Cannot assign to 'this.incEnabled + this.properties.itemIndex'.

I think I am trying to do something which I should not do. I am wondering whats oing wrong. I tried to assign a string value too as above variable is a string. Still the same error. Please suggest.

Thanks,
Sneha

Answer 1

There are two things in what you have written that do not seem right at all.

1. JavaScript Assignment Operator (=).

   This operator works by doing:

   a) Evaluates the expression from the right side of the '=' sign.
   b) Assigns the result to the left hand side expression.

   The problem in your example is (b), the expression on the left is not assignable because you are performing a sum (expressions which involve arithmetic operations are not assignable).

2. Global variable : this.decEnabled

   A global variable is a variable whose scope is the global scope, ie anyone can access that variable. You can define global variables in the global scope of the document by writing on the top of the document (or outside the scope of any function) the following:

    var global_var; 

   In your explanation you say that you are trying to create the global variable 'this.decEnabled'. However, this cannot be a global variable in any case because you are binding 'decEnabled' to a scope (in this case, you are referring to the current scope by using the 'this' operator).

The error that you are receiving is from (1).

If you are trying to compare values the equality operator that you are looking for is '==' or '==='.