ReferenceError: "x" is not defined

Message

ReferenceError: "x" is not defined

Error type

ReferenceError.

What went wrong?

There is a non-existent variable referenced somewhere. This variable needs to be declared, or you need make sure it is available in your current script or scope.

Examples

Variable not declared

foo.substring(1); // ReferenceError: foo is not defined

The "foo" variable isn't defined anywhere. It needs to be some string, so that the String.prototype.substring() method will work.

var foo = "bar";
foo.substring(1); // "ar"

Wrong scope

A variable need to be available in the current context of execution. Variables defined inside a function cannot be accessed from anywhere outside the function, because the variable is defined only in the scope of the function

function numbers () { 
  var num1 = 2, 
      num2 = 3;
  return num1 + num2;
}

console.log(num1); // ReferenceError num1 is not defined.

However, a function can access all variables and functions defined inside the scope in which it is defined. In other words, a function defined in the global scope can access all variables defined in the global scope.

var num1 = 2,
    num2 = 3;

function numbers () {
  return num1 + num2; 
}

console.log(num1); // 2

See also

• Scope
• Declaring variables in the JavaScript Guide
• Function scope in the JavaScript Guide