uncaught referenceerror assignment to undeclared variable

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JavaScript ReferenceError – Assignment to undeclared variable

This JavaScript exception Assignment to undeclared variable occurs in strict-mode If the value has been assigned to an undeclared variable.

Error Type:

Cause of the error: Somewhere in the code, there is an assignment without the var , let, or const keywords. When a value is assigned to an undeclared variable this error occurs.

Example 1: In this example, the const keyword is used with the variable assignment, So the error has not occurred.

Output:

Example 2: In this example, the var , let or const keyword is not used with the variable assignment, So the error has occurred.

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ReferenceError: assignment to undeclared variable "x"

Valid cases.

ReferenceError warning in strict mode only.

What went wrong?

A value has been assigned to an undeclared variable. In other words, there was an assignment without the var keyword. There are some differences between declared and undeclared variables, which might lead to unexpected results and that's why JavaScript presents an error in strict mode.

Three things to note about declared and undeclared variables:

Declared variables are constrained in the execution context in which they are declared. Undeclared variables are always global.
Declared variables are created before any code is executed. Undeclared variables do not exist until the code assigning to them is executed.
Declared variables are a non-configurable property of their execution context (function or global). Undeclared variables are configurable (e.g. can be deleted).

For more details and examples, see the var reference page.

Errors about undeclared variable assignments occur in strict mode code only. In non-strict code, they are silently ignored.

Invalid cases

In this case, the variable "bar" is an undeclared variable.

To make "bar" a declared variable, you can add the var keyword in front of it.

Strict mode

Document Tags and Contributors

ReferenceError
Strict Mode
JavaScript basics
JavaScript first steps
JavaScript building blocks
Introducing JavaScript objects
Introduction
Grammar and types
Control flow and error handling
Loops and iteration
Expressions and operators
Numbers and dates
Text formatting
Regular expressions
Indexed collections
Keyed collections
Working with objects
Details of the object model
Iterators and generators
Meta programming
A re-introduction to JavaScript
JavaScript data structures
Equality comparisons and sameness
Inheritance and the prototype chain
JavaScript typed arrays
Memory Management
Concurrency model and Event Loop
References:
ArrayBuffer
AsyncFunction
Float32Array
Float64Array
GeneratorFunction
InternalError
Intl.Collator
Intl.DateTimeFormat
Intl.NumberFormat
ParallelArray
SIMD.Bool16x8
SIMD.Bool32x4
SIMD.Bool64x2
SIMD.Bool8x16
SIMD.Float32x4
SIMD.Float64x2
SIMD.Int16x8
SIMD.Int32x4
SIMD.Int8x16
SIMD.Uint16x8
SIMD.Uint32x4
SIMD.Uint8x16
SharedArrayBuffer
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Uint16Array
Uint32Array
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decodeURI()
decodeURIComponent()
encodeURI()
encodeURIComponent()
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Conditional (ternary) Operator
Destructuring assignment
Expression closures
Generator comprehensions
Grouping operator
Legacy generator function expression
Logical Operators
Object initializer
Operator precedence
Property accessors
Spread syntax
async function expression
class expression
delete operator
function expression
function* expression
in operator
new operator
void operator
Legacy generator function
async function
for each...in
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Arrow functions
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constructor
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RangeError: invalid array length
RangeError: invalid date
RangeError: precision is out of range
RangeError: radix must be an integer
RangeError: repeat count must be less than infinity
RangeError: repeat count must be non-negative
ReferenceError: "x" is not defined
ReferenceError: assignment to undeclared variable "x"
ReferenceError: deprecated caller or arguments usage
ReferenceError: invalid assignment left-hand side
ReferenceError: reference to undefined property "x"
SyntaxError: "0"-prefixed octal literals and octal escape seq. are deprecated
SyntaxError: "use strict" not allowed in function with non-simple parameters
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SyntaxError: Using //@ to indicate sourceURL pragmas is deprecated. Use //# instead
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How to Fix the ‘ReferenceError: assignment to undeclared variable “x”‘ Error in Our JavaScript App?

Post author By John Au-Yeung
Post date August 20, 2021
No Comments on How to Fix the ‘ReferenceError: assignment to undeclared variable “x”‘ Error in Our JavaScript App?

Sometimes, we may run into the ‘ReferenceError: assignment to undeclared variable "x"’ when we’re developing JavaScript apps.

In this article, we’ll look at how to fix the ‘ReferenceError: assignment to undeclared variable "x"’ when we’re developing JavaScript apps.

Fix the ‘ReferenceError: assignment to undeclared variable "x"’ When Developing JavaScript Apps

To fix the ‘ReferenceError: assignment to undeclared variable "x"’ when we’re developing JavaScript apps, we should make sure that we’re assigning values to variables that have already been declared.

The error message for this error is ReferenceError: "x" is not defined in Chrome.

And in Edge, the error message for this error is ReferenceError: Variable undefined in strict mode .

For instance, we shouldn’t write code like:

since bar hasn’t been declared in the foo function.

Instead, we should declare the bar variable by writing:

Now the error should be fixed.

Sometimes, we may run into the 'ReferenceError: "x" is not defined' when we're developing JavaScript…

It is easy to convert anything a boolean in JavaScript. Truthy values will be converted…

To throw errors in our JavaScript apps, we usually through an object that’s the instance…

By John Au-Yeung

Web developer specializing in React, Vue, and front end development.

ReferenceError: assignment to undeclared variable "x"

The JavaScript strict mode -only exception "Assignment to undeclared variable" occurs when the value has been assigned to an undeclared variable.

ReferenceError warning in strict mode only.

What went wrong?

Three things to note about declared and undeclared variables:

Declared variables are constrained in the execution context in which they are declared. Undeclared variables are always global.
Declared variables are created before any code is executed. Undeclared variables do not exist until the code assigning to them is executed.
Declared variables are a non-configurable property of their execution context (function or global). Undeclared variables are configurable (e.g. can be deleted).

For more details and examples, see the var reference page.

Errors about undeclared variable assignments occur in strict mode code only. In non-strict code, they are silently ignored.

Invalid cases

In this case, the variable "bar" is an undeclared variable.

Valid cases

To make "bar" a declared variable, you can add the var keyword in front of it.

Strict mode

ReferenceError: assignment to undeclared variable "x"

The JavaScript strict mode -only exception "Assignment to undeclared variable" occurs when the value has been assigned to an undeclared variable.

ReferenceError in strict mode only.

What went wrong?

Three things to note about declared and undeclared variables:

Declared variables are constrained in the execution context in which they are declared. Undeclared variables are always global.
Declared variables are created before any code is executed. Undeclared variables do not exist until the code assigning to them is executed.
Declared variables are a non-configurable property of their execution context (function or global). Undeclared variables are configurable (e.g. can be deleted).

For more details and examples, see the var reference page.

Errors about undeclared variable assignments occur in strict mode code only. In non-strict code, they are silently ignored.

Invalid cases

In this case, the variable "bar" is an undeclared variable.

Valid cases

To make "bar" a declared variable, you can add a let , const , or var keyword in front of it.

Strict mode

分析出现ReferenceError: assignment to undeclared variable "x"的原因

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分析出现ReferenceError: assignment to undeclared variable "x"的原因。

我们在开发项目的时候，出现以下报错信息：

仅在严格模式中出现 ReferenceError 警告。

在代码里赋值了一个未声明的变量。换句话说，有处没有带着 var 关键字的赋值。事实上已声明的和未声明的变量之间有一些差异，这可能会导致意想不到的结果，这就是为什么 JavaScript 在严格模式打印出这种错误。

关于已声明和未声明的变量，其有三个注意事项：

已声明的变量被约束在其执行上下文中。未声明的变量总是全局的。

已声明的变量在执行任何代码之前就创建了。未声明的变量则不存在，直到执行相关的代码。

已声明的变量是其执行上下文（函数或全局）的不可配置属性。而未声明的变量是可配置的（例如可以删除）。

更多信息及例子，请参考 var 页面。

关于未声明变量的赋值的错误仅在严格模式里出现。在非严格模式中，这些将被忽略。

在本例中，"bar" 是未声明的变量。

为了使 "bar" 是一个已声明变量，你需要在其前面加一个 var 关键字。

※大家的支持是我们创作的动力！

What went wrong?

ReferenceError warning in strict mode only.

Three things to note about declared and undeclared variables:

Declared variables are constrained in the execution context in which they are declared. Undeclared variables are always global.
Declared variables are created before any code is executed. Undeclared variables do not exist until the code assigning to them is executed.
Declared variables are a non-configurable property of their execution context (function or global). Undeclared variables are configurable (e.g. can be deleted).

For more details and examples, see the var reference page.

Errors about undeclared variable assignments occur in strict mode code only. In non-strict code, they are silently ignored.

Invalid cases

In this case, the variable "bar" is an undeclared variable.

Valid cases

To make "bar" a declared variable, you can add the var keyword in front of it.

Strict mode

Document Tags and Contributors

ReferenceError
Strict Mode
JavaScript basics
JavaScript first steps
JavaScript building blocks
Introducing JavaScript objects
Introduction
Grammar and types
Control flow and error handling
Loops and iteration
Expressions and operators
Numbers and dates
Text formatting
Regular expressions
Indexed collections
Keyed collections
Working with objects
Details of the object model
Using promises
Iterators and generators
Meta programming
Client-side web APIs
A re-introduction to JavaScript
JavaScript data structures
Equality comparisons and sameness
Inheritance and the prototype chain
JavaScript typed arrays
Memory Management
Concurrency model and Event Loop
References:
ArrayBuffer
AsyncFunction
Float32Array
Float64Array
GeneratorFunction
InternalError
Intl.Collator
Intl.DateTimeFormat
Intl.ListFormat
Intl.NumberFormat
Intl.PluralRules
Intl.RelativeTimeFormat
SharedArrayBuffer
SyntaxError
Uint16Array
Uint32Array
Uint8ClampedArray
WebAssembly
decodeURI()
decodeURIComponent()
encodeURI()
encodeURIComponent()
parseFloat()
Arithmetic operators
Array comprehensions
Assignment operators
Bitwise operators
Comma operator
Comparison operators
Conditional (ternary) operator
Destructuring assignment
Expression closures
Generator comprehensions
Grouping operator
Legacy generator function expression
Logical operators
Object initializer
Operator precedence
(currently at stage 1) allows the creation of chained function calls in a readable manner. Basically, the pipeline operator provides syntactic sugar on a function call with a single argument allowing you to write">Pipeline operator
Property accessors
Spread syntax
async function expression
class expression
delete operator
function expression
function* expression
in operator
new operator
void operator
Legacy generator function
async function
for await...of
for each...in
function declaration
import.meta
try...catch
Arrow functions
Default parameters
Method definitions
Rest parameters
The arguments object
constructor
element loaded from a different domain for which you violated the same-origin policy.">Error: Permission denied to access property "x"
InternalError: too much recursion
RangeError: argument is not a valid code point
RangeError: invalid array length
RangeError: invalid date
RangeError: precision is out of range
RangeError: radix must be an integer
RangeError: repeat count must be less than infinity
RangeError: repeat count must be non-negative
ReferenceError: "x" is not defined
ReferenceError: can't access lexical declaration`X' before initialization
ReferenceError: deprecated caller or arguments usage
ReferenceError: invalid assignment left-hand side
ReferenceError: reference to undefined property "x"
SyntaxError: "0"-prefixed octal literals and octal escape seq. are deprecated
SyntaxError: "use strict" not allowed in function with non-simple parameters
SyntaxError: "x" is a reserved identifier
SyntaxError: JSON.parse: bad parsing
SyntaxError: Malformed formal parameter
SyntaxError: Unexpected token
SyntaxError: Using //@ to indicate sourceURL pragmas is deprecated. Use //# instead
SyntaxError: a declaration in the head of a for-of loop can't have an initializer
SyntaxError: applying the 'delete' operator to an unqualified name is deprecated
SyntaxError: for-in loop head declarations may not have initializers
SyntaxError: function statement requires a name
SyntaxError: identifier starts immediately after numeric literal
SyntaxError: illegal character
SyntaxError: invalid regular expression flag "x"
SyntaxError: missing ) after argument list
SyntaxError: missing ) after condition
SyntaxError: missing : after property id
SyntaxError: missing ; before statement
SyntaxError: missing = in const declaration
SyntaxError: missing ] after element list
SyntaxError: missing formal parameter
SyntaxError: missing name after . operator
SyntaxError: missing variable name
SyntaxError: missing } after function body
SyntaxError: missing } after property list
SyntaxError: redeclaration of formal parameter "x"
SyntaxError: return not in function
SyntaxError: test for equality (==) mistyped as assignment (=)?
SyntaxError: unterminated string literal
TypeError: "x" has no properties
TypeError: "x" is (not) "y"
TypeError: "x" is not a constructor
TypeError: "x" is not a function
TypeError: "x" is not a non-null object
TypeError: "x" is read-only
TypeError: 'x' is not iterable
TypeError: More arguments needed
TypeError: Reduce of empty array with no initial value
TypeError: can't access dead object
TypeError: can't access property "x" of "y"
TypeError: can't define property "x": "obj" is not extensible
TypeError: can't delete non-configurable array element
TypeError: can't redefine non-configurable property "x"
TypeError: cannot use 'in' operator to search for 'x' in 'y'
TypeError: cyclic object value
TypeError: invalid 'instanceof' operand 'x'
TypeError: invalid Array.prototype.sort argument
TypeError: invalid arguments
TypeError: invalid assignment to const "x"
TypeError: property "x" is non-configurable and can't be deleted
TypeError: setting getter-only property "x"
TypeError: variable "x" redeclares argument
URIError: malformed URI sequence
Warning: -file- is being assigned a //# sourceMappingURL, but already has one
Warning: 08/09 is not a legal ECMA-262 octal constant
Warning: Date.prototype.toLocaleFormat is deprecated
Warning: JavaScript 1.6's for-each-in loops are deprecated
Warning: String.x is deprecated; use String.prototype.x instead
Warning: expression closures are deprecated
Warning: unreachable code after return statement
X.prototype.y called on incompatible type
JavaScript technologies overview
Lexical grammar
Enumerability and ownership of properties
Iteration protocols
Transitioning to strict mode
Template literals
Deprecated features
ECMAScript 2015 support in Mozilla
ECMAScript 5 support in Mozilla
ECMAScript Next support in Mozilla
Firefox JavaScript changelog
New in JavaScript 1.1
New in JavaScript 1.2
New in JavaScript 1.3
New in JavaScript 1.4
New in JavaScript 1.5
New in JavaScript 1.6
New in JavaScript 1.7
New in JavaScript 1.8
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Documentation:
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Properties index
Pages tagged "JavaScript"
JavaScript doc status
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ReferenceError: assignment to undeclared variable "x"

ReferenceError warning in strict mode only.

What went wrong?

Three things to note about declared and undeclared variables:

Declared variables are constrained in the execution context in which they are declared. Undeclared variables are always global.
Declared variables are created before any code is executed. Undeclared variables do not exist until the code assigning to them is executed.
Declared variables are a non-configurable property of their execution context (function or global). Undeclared variables are configurable (e.g. can be deleted).

For more details and examples, see the var reference page.

Errors about undeclared variable assignments occur in strict mode code only. In non-strict code, they are silently ignored.

Invalid cases

In this case, the variable "bar" is an undeclared variable.

Valid cases

To make "bar" a declared variable, you can add the var keyword in front of it.

Strict mode

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Uncaught ReferenceError; assignmen to undeclared variable on Parcel BUILD #8539

kordou commented Oct 13, 2022

mischnic commented Oct 13, 2022

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COMMENTS

ReferenceError: assignment to undeclared variable "x"
Declared variables are a non-configurable property of their execution context (function or global). Undeclared variables are configurable (e.g. can be deleted). For more details and examples, see the var reference page. Errors about undeclared variable assignments occur in strict mode code only. In non-strict code, they are silently ignored.
"assignment to undeclared variable" when using "for (i=0; ..)"
ReferenceError: Variable undefined in strict mode (Edge) Invalid cases In this case, the variable "bar" is an undeclared variable. function foo() { 'use strict'; bar = true; } foo(); // ReferenceError: assignment to undeclared variable bar Valid cases To make "bar" a declared variable, you can add the var keyword in front of it. function foo ...
JavaScript ReferenceError
This JavaScript exception Assignment to undeclared variable occurs in strict-mode If the value has been assigned to an undeclared variable. Message: ReferenceError: assignment to undeclared variable "x" (Firefox) ReferenceError: "x" is not defined (Chrome) ReferenceError: Variable undefined in strict mode (Edge)
ReferenceError: assignment to undeclared variable "x"
Declared variables are a non-configurable property of their execution context (function or global). Undeclared variables are configurable (e.g. can be deleted). For more details and examples, see the var reference page. Errors about undeclared variable assignments occur in strict mode code only. In non-strict code, they are silently ignored.
How to Fix the 'ReferenceError: assignment to undeclared variable "x
Fix the 'ReferenceError: assignment to undeclared variable "x"' When Developing JavaScript Apps. To fix the 'ReferenceError: assignment to undeclared variable "x"' when we're developing JavaScript apps, we should make sure that we're assigning values to variables that have already been declared.
A Comprehensive Guide on Reference Error: JavaScript
When any value is assigned to undeclared variable or assignment without the var keyword or variable is not in your current scope, it might lead to unexpected results and that's why JavaScript presents a ReferenceError: assignment to undeclared variable "x" in strict mode. ... it might lead to unexpected results and that's why JavaScript ...
Errors: Undeclared var
Declared variables are a non-configurable property of their execution context (function or global). Undeclared variables are configurable (e.g. can be deleted). For more details and examples, see the var reference page. Errors about undeclared variable assignments occur in strict mode code only. In non-strict code, they are silently ignored.
Errors: Undeclared Var
Declared variables are a non-configurable property of their execution context (function or global). Undeclared variables are configurable (e.g. can be deleted). For more details and examples, see the var reference page. Errors about undeclared variable assignments occur in strict mode code only. In non-strict code, they are silently ignored.
分析出现ReferenceError: assignment to undeclared variable "x"的原因
关键词： js. 分析出现ReferenceError: assignment to undeclared variable "x"的原因。. 我们在开发项目的时候，出现以下报错信息：. ReferenceError: assignment to undeclared variable "x" (Firefox) ReferenceError: "x" is not defined (Chrome) ReferenceError: Variable undefined in strict mode (Edge)
ReferenceError: assignment to undeclared variable "x"
Declared variables are a non-configurable property of their execution context (function or global). Undeclared variables are configurable (e.g. can be deleted). For more details and examples, see the var reference page. Errors about undeclared variable assignments occur in strict mode code only. In non-strict code, they are silently ignored.
ReferenceError: assignment to undeclared variable "x"
Declared variables are a non-configurable property of their execution context (function or global). Undeclared variables are configurable (e.g. can be deleted). For more details and examples, see the var reference page. Errors about undeclared variable assignments occur in strict mode code only. In non-strict code, they are silently ignored.
Rectangle display bug when drawing in 1.0.3 or 1.0.4
Before you do that, verify that none of your dependencies uses this variable!To do so, run your app, open console and type window.type.If it outputs something different from undefined, find and get rid of the library that uses this variable or switch to another drawing library (for example, geoman).. This trick works for my build process, though, you might want to modify it for your build system.
ReferenceError: assignment to undeclared variable "x"
ReferenceError: "x" is not defined; ReferenceError: assignment to undeclared variable "x" ReferenceError: can't access lexical declaration`X' before initialization; ReferenceError: deprecated caller or arguments usage; ReferenceError: reference to undefined property "x" SyntaxError: "0"-prefixed octal literals and octal escape seq. are deprecated
Uncaught ReferenceError: assignment to undeclared variable i #26
for (i = 0;,,,) {} // << uses the local variable} Unlike the initial report, this pattern should not cause any issues as each var creates a function-level scope and do not mess with globals. So there is no real need "fix" what is not broken.
TypeError: invalid assignment to const "x"
The const declaration creates a read-only reference to a value. It does not mean the value it holds is immutable, just that the variable identifier cannot be reassigned. For instance, in case the content is an object, this means the object itself can still be altered. This means that you can't mutate the value stored in a variable: js.
Uncaught ReferenceError; assignmen to undeclared variable on Parcel
"Uncaught ReferenceError; assignmen to undeclared variable" basically i can understanth that my custom Classes are not included. i also tried one version of parcel down but still the same issue. The text was updated successfully, but these errors were encountered:
[Vue warn]: Error in v-on handler: "ReferenceError: assignment to
data() is ran very early in your component initialization. It sets the reactive properties (what Vue will listen and react to, throughout the component's lifecycle). At that point, you can't even access previously defined properties in data() (i.e: this.options in your case), nevermind a property which is just being declared. You probably want to change orders: this.orders to orders: [] and ...
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Uncaught ReferenceError: _ is not defined (lodash
Lodash - difference between .extend() / .assign() and .merge() 229 React Uncaught ReferenceError: process is not defined. 220 ... ReactJS: Uncaught ReferenceError: [variable] not defined. 1 Uncaught ReferenceError: require is not defined in ReactJS Scripts. 1 React.js "Uncaught ReferenceError: exports is not defined" 501

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JavaScript ReferenceError – Assignment to undeclared variable

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Uncaught ReferenceError; assignmen to undeclared variable on Parcel BUILD #8539

kordou commented Oct 13, 2022

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