Question

I was reading ECMA 5 262, and feel confused on the term “strict reference” in http://es5.github.com/#IsStrictReference:

A Reference is a resolved name binding. A Reference consists of three components, the base value, the referenced name and the Boolean valued strict reference flag. The base value is either undefined, an Object, a Boolean, a String, a Number, or an environment record (10.2.1). A base value of undefined indicates that the reference could not be resolved to a binding. The referenced name is a String.

There’s not much description on it. The only related operation on Reference is

IsStrictReference(V). Returns the strict reference component of the reference V.

but no operation to set, neither description how we can decide the value.

I guess it must be related to the strict mode, but how can i tell what’s the value for a specific Reference?

Answer 1

As far as I understand, it’s a property for references set to true when using references with strict mode in ECMAScript 5 (aka ES5) initialized. When strict mode is set, more operations will lead to errors (syntax, reference, for example initializing a variable without the var keyword). See the MDN-documentation for more on strict mode.

[edit] based on comment
I think it’s for the scope where strict mode is defined. So in

function strict()
{ 'use strict';
  // from here on and within the function
  // IsStrictReference is true
  showme = "Am I defined?";
  return "Hi!  I'm a strict mode function!  " + showme;
}

function nonstrict()
{ 
  // IsStrictReference is ... well, undefined I suppose, or false by default
  showme2 = "Am I defined?";
  return "Hi!  I'm NOT a strict mode function!  " + showme2;
}
strict(); //=> ReferenceError: showme is not defined
notstrict(); //=> "Hi!  I'm NOT a strict mode function! Am I defined?"

Executing strict() throws a ReferenceError, but nonstrict() doesn’t. If you had placed the use strict-statement outside the function blocks, executing both functions would throw a ReferenceError.