y
    }
    

###  void operator and undefined

The [ ` void ` ](/en-US/docs/Web/JavaScript/Reference/Operators/void) operator
is a third alternative.

js

    
    
    let x;
    if (x === void 0) {
      // these statements execute
    }
    
    // y has not been declared before
    if (y === void 0) {
      // throws Uncaught ReferenceError: y is not defined
    }
    

##  Specifications

Specification  
---  
[ ECMAScript Language Specification  
#  sec-undefined  ](https://tc39.es/ecma262/multipage/global-object.html#sec-
undefined)  
  
##  Browser compatibility

BCD tables only load in the browser  with JavaScript enabled. Enable
JavaScript to view data.

##  See also

  * [ JavaScript data types and data structures ](/en-US/docs/Web/JavaScript/Data_structures)
  * [ ` null ` ](/en-US/docs/Web/JavaScript/Reference/Operators/null)

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