- Assignment to property of function parameter no-param-reassign
Last updated: Mar 7, 2024 Reading time · 3 min
# Table of Contents
- Disabling the no-param-reassign ESLint rule for a single line
- Disabling the no-param-reassign ESLint rule for an entire file
- Disabling the no-param-reassign ESLint rule globally
# Assignment to property of function parameter no-param-reassign
The ESLint error "Assignment to property of function parameter 'X' eslint no-param-reassign" occurs when you try to assign a property to a function parameter.
To solve the error, disable the ESLint rule or create a new object based on the parameter to which you can assign properties.
Here is an example of how the error occurs.
The ESLint rule forbids assignment to function parameters because modifying a function's parameters also mutates the arguments object and can lead to confusing behavior.
One way to resolve the issue is to create a new object to which you can assign properties.
We used the spread syntax (...) to unpack the properties of the function parameter into a new object to which we can assign properties.
If you need to unpack an array, use the following syntax instead.
The same approach can be used if you simply need to assign the function parameter to a variable so you can mutate it.
We declared the bar variable using the let keyword and set it to the value of the foo parameter.
We are then able to reassign the bar variable without any issues.
# Disabling the no-param-reassign ESLint rule for a single line
You can use a comment if you want to disable the no-param-reassign ESLint rule for a single line.
Make sure to add the comment directly above the assignment that causes the error.
# Disabling the no-param-reassign ESLint rule for an entire file
You can also use a comment to disable the no-param-reassign ESLint rule for an entire file.
Make sure to add the comment at the top of the file or at least above the function in which you reassign parameters.
The same approach can be used to disable the rule only for a single function.
The first comment disables the no-param-reassign rule and the second comment enables it.
If you try to reassign a parameter after the second comment, you will get an ESLint error.
# Disabling the no-param-reassign ESLint rule globally
If you need to disable the no-param-reassign rule globally, you have to edit your .eslintrc.js file.
If you only want to be able to assign properties to an object parameter, set props to false instead of disabling the rule completely.
The following code is valid after making the change.
If you use a .eslintrc or .eslintrc.json file, make sure to double-quote the properties and values.
If you want to only allow assignment to object parameters, use the following line instead.
Make sure all properties are double-quoted and there are no trailing commas if your config is written in JSON.
# Additional Resources
You can learn more about the related topics by checking out the following tutorials:
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- Plugin "react" was conflicted between package.json » eslint-config-react-app
- React: Unexpected use of 'X' no-restricted-globals in ESLint
- TypeScript ESLint: Unsafe assignment of an any value [Fix]
- ESLint error Unary operator '++' used no-plusplus [Solved]
- ESLint Prefer default export import/prefer-default-export
- Arrow function should not return assignment. eslint no-return-assign
- TypeError: Cannot redefine property: X in JavaScript [Fixed]
- ESLint: disable multiple rules or a rule for multiple lines
- Expected linebreaks to be 'LF' but found 'CRLF' linebreak-style
- Missing return type on function TypeScript ESLint error
Borislav Hadzhiev
Web Developer
Copyright © 2024 Borislav Hadzhiev
Disallow Reassignment of Function Parameters (no-param-reassign)
Assignment to variables declared as function parameters can be misleading and lead to confusing behavior, as modifying function parameters will also mutate the arguments object. Often, assignment to function parameters is unintended and indicative of a mistake or programmer error.
This rule can be also configured to fail when function parameters are modified. Side effects on parameters can cause counter-intuitive execution flow and make errors difficult to track down.
Rule Details
This rule aims to prevent unintended behavior caused by modification or reassignment of function parameters.
Examples of incorrect code for this rule:
Examples of correct code for this rule:
This rule takes one option, an object, with a boolean property "props" , and arrays "ignorePropertyModificationsFor" and "ignorePropertyModificationsForRegex" . "props" is false by default. If "props" is set to true , this rule warns against the modification of parameter properties unless they're included in "ignorePropertyModificationsFor" or "ignorePropertyModificationsForRegex" , which is an empty array by default.
Examples of correct code for the default { "props": false } option:
Examples of incorrect code for the { "props": true } option:
Examples of correct code for the { "props": true } option with "ignorePropertyModificationsFor" set:
Examples of correct code for the { "props": true } option with "ignorePropertyModificationsForRegex" set:
When Not To Use It
If you want to allow assignment to function parameters, then you can safely disable this rule.
Further Reading
- JavaScript: Don’t Reassign Your Function Arguments
This rule was introduced in ESLint 0.18.0.
- Rule source
- Documentation source
© OpenJS Foundation and other contributors Licensed under the MIT License. https://eslint.org/docs/rules/no-param-reassign
no-param-reassign
Disallow reassigning function parameters
Assignment to variables declared as function parameters can be misleading and lead to confusing behavior, as modifying function parameters will also mutate the arguments object. Often, assignment to function parameters is unintended and indicative of a mistake or programmer error.
This rule can be also configured to fail when function parameters are modified. Side effects on parameters can cause counter-intuitive execution flow and make errors difficult to track down.
Rule Details
This rule aims to prevent unintended behavior caused by modification or reassignment of function parameters.
Examples of incorrect code for this rule:
Examples of correct code for this rule:
This rule takes one option, an object, with a boolean property "props" , and arrays "ignorePropertyModificationsFor" and "ignorePropertyModificationsForRegex" . "props" is false by default. If "props" is set to true , this rule warns against the modification of parameter properties unless they’re included in "ignorePropertyModificationsFor" or "ignorePropertyModificationsForRegex" , which is an empty array by default.
Examples of correct code for the default { "props": false } option:
Examples of incorrect code for the { "props": true } option:
Examples of correct code for the { "props": true } option with "ignorePropertyModificationsFor" set:
Examples of correct code for the { "props": true } option with "ignorePropertyModificationsForRegex" set:
When Not To Use It
If you want to allow assignment to function parameters, then you can safely disable this rule.
This rule was introduced in ESLint v0.18.0.
Further Reading
JavaScript: Don’t Reassign Your Function Arguments
- Rule source
- Tests source
© OpenJS Foundation and other contributors Licensed under the MIT License. https://eslint.org/docs/latest/rules/no-param-reassign
How to avoid no-param-reassign ESLint error when setting a property on a DOM object with JavaScript?
- Post author By John Au-Yeung
- Post date April 28, 2022
- No Comments on How to avoid no-param-reassign ESLint error when setting a property on a DOM object with JavaScript?
Sometimes, we want to avoid no-param-reassign ESLint error when setting a property on a DOM object with JavaScript.
In thiks article, we’ll look at how to avoid no-param-reassign ESLint error when setting a property on a DOM object with JavaScript.
To avoid no-param-reassign ESLint error when setting a property on a DOM object with JavaScript, we can assign the parameter to a variable.
For instance, we write
to create the f function.
In it, we assign el to the theElement variable.
And then we add the theElement.expand property to it.
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Web developer specializing in React, Vue, and front end development.
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Disallow Reassignment of Function Parameters (no-param-reassign)
Assignment to variables declared as function parameters can be misleading and lead to confusing behavior, as modifying function parameters will also mutate the arguments object. Often, assignment to function parameters is unintended and indicative of a mistake or programmer error.
This rule can be also configured to fail when function parameters are modified. Side effects on parameters can cause counter-intuitive execution flow and make errors difficult to track down.
Rule Details
This rule aims to prevent unintended behavior caused by modification or reassignment of function parameters.
Examples of incorrect code for this rule:
Examples of correct code for this rule:
This rule takes one option, an object, with a boolean property "props" and an array "ignorePropertyModificationsFor" . "props" is false by default. If "props" is set to true , this rule warns against the modification of parameter properties unless they're included in "ignorePropertyModificationsFor" , which is an empty array by default.
Examples of correct code for the default { "props": false } option:
Examples of incorrect code for the { "props": true } option:
Examples of correct code for the { "props": true } option with "ignorePropertyModificationsFor" set:
When Not To Use It
If you want to allow assignment to function parameters, then you can safely disable this rule.
Further Reading
- JavaScript: Don’t Reassign Your Function Arguments
This rule was introduced in ESLint 0.18.0.
- Rule source
- Documentation source
Disallow Reassignment of Function Parameters (no-param-reassign)
Assignment to variables declared as function parameters can be misleading and lead to confusing behavior, as modifying function parameters will also mutate the arguments object. Often, assignment to function parameters is unintended and indicative of a mistake or programmer error.
This rule can be also configured to fail when function parameters are modified. Side effects on parameters can cause counter-intuitive execution flow and make errors difficult to track down.
Rule Details
This rule aims to prevent unintended behavior caused by modification or reassignment of function parameters.
Examples of incorrect code for this rule:
Examples of correct code for this rule:
This rule takes one option, an object, with a boolean property "props" and an array "ignorePropertyModificationsFor" . "props" is false by default. If "props" is set to true , this rule warns against the modification of parameter properties unless they’re included in "ignorePropertyModificationsFor" , which is an empty array by default.
Examples of correct code for the default { "props" : false } option:
Examples of incorrect code for the { "props" : true } option:
Examples of correct code for the { "props" : true } option with "ignorePropertyModificationsFor" set:
When Not To Use It
If you want to allow assignment to function parameters, then you can safely disable this rule.
Further Reading
- JavaScript: Don’t Reassign Your Function Arguments
This rule was introduced in ESLint 0.18.0.
- Rule source
- Documentation source
Disallow Reassignment of Function Parameters (no-param-reassign)
Assignment to variables declared as function parameters can be misleading and lead to confusing behavior, as modifying function parameters will also mutate the arguments object. Often, assignment to function parameters is unintended and indicative of a mistake or programmer error.
This rule can be also configured to fail when function parameters are modified. Side effects on parameters can cause counter-intuitive execution flow and make errors difficult to track down.
Rule Details
This rule aims to prevent unintended behavior caused by modification or reassignment of function parameters.
Examples of incorrect code for this rule:
Examples of correct code for this rule:
This rule takes one option, an object, with a boolean property "props" and an array "ignorePropertyModificationsFor" . "props" is false by default. If "props" is set to true , this rule warns against the modification of parameter properties unless they’re included in "ignorePropertyModificationsFor" , which is an empty array by default.
Examples of correct code for the default { "props": false } option:
Examples of incorrect code for the { "props": true } option:
Examples of correct code for the { "props": true } option with "ignorePropertyModificationsFor" set:
When Not To Use It
If you want to allow assignment to function parameters, then you can safely disable this rule.
Further Reading
- JavaScript: Don’t Reassign Your Function Arguments
This rule was introduced in ESLint 0.18.0.
- Rule source
- Documentation source
no-param-reassign
Disallow reassigning function parameters
对作为函数参数声明的变量进行赋值可能会产生误导并导致混乱的行为，因为修改函数参数也会改变 arguments 对象。通常情况下，对函数参数的赋值是无意的，表明了一个错误或程序员的错误。
这条规则也可以被配置为在修改函数参数时失败。参数的副作用会导致反直觉的执行流程，使错误难以追踪。
这条规则的目的是防止因修改或重新分配函数参数而引起的非预期行为。
使用此规则的 错误 示例：
使用此规则的 正确 示例：
这个规则有一个选项，是一个对象，有一个布尔属性 "props" 和数组 "ignorePropertyModificationsFor" 和 "ignorePropertyModificationsForRegex" 。 "props" 默认为 false 。如果 "props" 设置为 true ，本规则警告不要修改参数属性，除非它们被包含在 "ignorePropertyModificationsFor" 或 "ignorePropertyModificationsForRegex" 中，默认为空数组。
使用默认的 { "props": false } 选项的 正确 示例：
使用 { "props": true } 选项的 错误 示例：
设置了 "ignorePropertyModificationsFor" 的 { "props": true } 选项的**正确的代码示例：
设置了 "ignorePropertyModificationsForRegex" 的 { "props": true } 选项的**正确的代码示例：
如果你想允许对函数参数进行赋值，你可以安全地禁用此规则。
This rule was introduced in ESLint v0.18.0.
Further Reading
- Rule source
- Tests source
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TypeScript Reactjs: Assignment to property of function parameter 'state' #13253
sptGabriel commented May 3, 2020
anikethsaha commented May 3, 2020
Sorry, something went wrong.
sptGabriel commented May 3, 2020 • edited
eslint-deprecated bot commented Jun 4, 2020
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COMMENTS
This is a common ESLint issue that appears frequently on old codebase. You have modified the result variable which was passed as parameter. This behavior is prohibited by the rule. To resolve it, copy the argument to a temporary variable and work on it instead: export const fn = article => article.categoryValueDtoSet.reduce((res, item) => {.
The no-param-reassign warning makes sense for common functions, but for a classic Array.forEach loop over an array which you intend to mutate it isn't to appropriate. However, to get around this, you can also use Array.map with a new object (if you are like me, dislike snoozing warnings with comments): someArray = someArray.map((_item) => {.
If you want to allow assignment to function parameters, then you can safely disable this rule. Strict mode code doesn't sync indices of the arguments object with each parameter binding. Therefore, this rule is not necessary to protect against arguments object mutation in ESM modules or other strict mode functions. Version
function createEmployee(emp) { // ⛔️ Assignment to property of function parameter 'emp'. eslint no-param-reassign. emp.name = 'bobby hadz'; emp.salary = 500; return emp; } The ESLint rule forbids assignment to function parameters because modifying a function's parameters also mutates the arguments object and can lead to confusing behavior.
A pluggable and configurable linter tool for identifying and reporting on patterns in JavaScript. Maintain your code quality with ease.
Disallow Reassignment of Function Parameters (no-param-reassign) Assignment to variables declared as function parameters can be misleading and lead to confusing behavior, as modifying function parameters will also mutate the arguments object. ... Disallow Reassignment of Function Parameters (no-param-reassign) Assignment to variables declared ...
Rule Details. This rule aims to prevent unintended behavior caused by modification or reassignment of function parameters. Examples of incorrect code for this rule: /*eslint no-param-reassign: "error"*/ function foo(bar) {. bar = 13; } function foo(bar) {. bar++; } function foo(bar) { for (bar in baz) {} } function foo(bar) { for (bar of baz) {} }
Spread the love Related Posts What's the Difference Between the tagName and nodeName Property of a DOM Node in JavaScript?In a DOM node object, we see the tagName and nodeName property when we inspect… How to Add Property to an Object in JavascriptThere're a few ways to add properties to an object in JavaScript. One […]
It's not a conflict so much as an exception: We enforce that property reassignment is enforced by no-param-reassign except properties of the identifiers named in the option. Yes, you've understood the example correctly. And yes, props: true would be necessary for this to even come into effect (assuming props is normally false by default).
Disallow Reassignment of Function Parameters (no-param-reassign) Assignment to variables declared as function parameters can be misleading and lead to confusing ... /*eslint no-param-reassign: "error"*/ function foo ... an object, with a boolean property "props" and an array "ignorePropertyModificationsFor". "props" is false by default. If ...
eslint output: Assignment to function parameter 'line' no-param-reassign. In such cases creation an intermediate variable could be overcomplication. May be some additions to the rule like proxyTraps: false, eventListeners: false would be helpful.
Thanks @ilyavolodin.I meant a function-level comment like // eslint-disable-func no-param-reassign to disable the check for the entire function (or block) that line was found in.. Anyway, compared to your solution, my proposal would only save one line of comments, so probably the current way to wrap the function between /* eslint-disable no-param-reassign */ and /* eslint-enable */ is good enough.
Disallow Reassignment of Function Parameters (no-param-reassign) Assignment to variables declared as function parameters can be misleading and lead to confusing ... /*eslint no-param-reassign: "error"*/ function foo ... with a boolean property "props" and an array "ignorePropertyModificationsFor". "props" is false by default. If "props" is set ...
Disallow Reassignment of Function Parameters (no-param-reassign) Assignment to variables declared as function parameters can be misleading and lead to confusing ... /*eslint no-param-reassign: "error"*/ function foo ... with a boolean property "props" and an array "ignorePropertyModificationsFor". "props" is false by default. If "props" is set ...
You can assign recurrence to a const variable in side the function and use that in side the function. onUpdateRecurrence = (recurrence) => { const recurrenceValue = {...recurrence}; //Your Code }
对作为函数参数声明的变量进行赋值可能会产生误导并导致混乱的行为，因为修改函数参数也会改变 arguments 对象。 通常情况下，对函数参数的赋值是无意的，表明了一个错误或程序员的错误。
A pluggable and configurable linter tool for identifying and reporting on patterns in JavaScript. Maintain your code quality with ease.
You are changing the event as soon as brought in.. Try this: events.map(e => { var event = e; event.createdDateTimeConverted = dateFunctions.formatDate( event ...
I just had this idea when another user tried to assign to the state function argument. There is actually an eslint rule for that: no-param-reassign. I'd suggest we either add that rule as a recommendation somehwere in the docs or go even one step farther and create a shareable config package .. That way we could add some more recommended rules in the future.
Assignment to property of function parameter 'a' Eslint. ... Assignment to property of function parameter (no-param-reassign) 2 ... Argument expression expected. eslint" with Typescript map function in React. 0 Fixing no-param-reassign Eslint issue in function. 6 ...
Hello I have a problem in my estlint: Assignment to property of function parameter 'state'. eslintno-param-reassign on this code: state.sideisOpen = action.payload; interface SideBar { sideisOpen: boolean; } const INITIAL_STATE: SideBar ...