ReferenceError: "x" is not defined
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The JavaScript exception "variable is not defined" occurs when there is a non-existent variable referenced somewhere.
Message#
ReferenceError: "x" is not defined (V8-based & Firefox)
ReferenceError: Can't find variable: x (Safari)
Error type#
{{jsxref("ReferenceError")}}.
What went wrong?#
There is a non-existent variable referenced somewhere. This variable needs to be declared, or you need to make sure it is available in your current script or scope.
[!NOTE] When loading a library (such as jQuery), make sure it is loaded before you access library variables, such as "$". Put the {{HTMLElement("script")}} element that loads the library before your code that uses it.
Examples#
Variable not declared#
```js example-bad foo.substring(1); // ReferenceError: foo is not defined
The "foo" variable isn't defined anywhere. It needs to be some string, so that the
{{jsxref("String.prototype.substring()")}} method will work.
```js example-good
const foo = "bar";
foo.substring(1); // "ar"
Wrong scope#
A variable needs 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
```js example-bad function numbers() { const num1 = 2; const 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.
```js example-good
const num1 = 2;
const num2 = 3;
function numbers() {
return num1 + num2;
}
console.log(numbers()); // 5