在 DOM 对象上设置属性时如何避免无参数重新分配

Question

I have a method which's main purpose is to set a property on a DOM object

function (el) {
  el.expando = {};
}

I use AirBnB's code style which makes ESLint throw a no-param-reassign error:

error Assignment to function parameter 'el' no-param-reassign

How can I manipulate a DOM object passed as an argument while conforming AirBnB's code style?

Somebody suggested to use /* eslint react/prop-types: 0 */ referring to another issue but if I am not mistaken this applies well for react, but not for native DOM manipulation.

Also I do not think changing the code style is an answer. I believe one of the benefits of using a standard style is having consistent code across projects and changing the rules at will feels like a misuse of a major code style like AirBnB's.

For the record, I asked AirBnB on GitHub, what they think is the way to go in these cases in issue #766 .

Answer 1

As @Mathletics suggests, you candisable the rule entirely by adding this to your .eslintrc.json file:

"rules": {
  "no-param-reassign": 0
}

Or you could disable the rule specifically for param properties

"rules": {
  "no-param-reassign": [2, { "props": false }]
}

Alternatively, you could disable the rule for that function

/* eslint-disable no-param-reassign */
function (el) {
  el.expando = {};
}
/* eslint-enable no-param-reassign */

Or for that line only

function (el) {
  el.expando = {}; // eslint-disable-line no-param-reassign
}

Answer 2

As this article explains , this rule is meant to avoid mutating the arguments object . If you assign to a parameter and then try and access some of the parameters via the arguments object, it can lead to unexpected results.

You could keep the rule intact and maintain the AirBnB style by using another variable to get a reference to the DOM element and then modify that:

function (el) {
  var theElement = el;
  theElement.expando = {};
}

In JS objects (including DOM nodes) are passed by reference, so here el and theElement are references to the same DOM node, but modifying theElement doesn't mutate the arguments object since arguments[0] remains just a reference to that DOM element.

This approach is hinted at in the documentation for the rule :

Examples of correct code for this rule:

/*eslint no-param-reassign: "error"*/

function foo(bar) {
    var baz = bar;
}

Personally, I would just use the "no-param-reassign": ["error", { "props": false }] approach a couple of other answers mentioned. Modifying a property of the parameter doesn't mutate what that parameter refers to and shouldn't run into the kinds of problems this rule is trying to avoid.

Answer 3

You can override this rule inside your .eslintrc file and disable it for param properties like this

{
    "rules": {
        "no-param-reassign": [2, { 
            "props": false
        }]
    },
    "extends": "eslint-config-airbnb"
}

This way rule is still active but it will not warn for properties. More info: http://eslint.org/docs/rules/no-param-reassign

Answer 4

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) => {
    let item = Object.assign({}, _item); // decouple instance
    item.foo = "bar"; // assign a property
    return item; // replace original with new instance
});

Answer 5

function (el) {
  el.setAttribute('expando', {});
}

Everything else is just ugly hacks.

Answer 6

那些希望有选择地停用此规则的人可能会对no-param-reassign规则的拟议新选项感兴趣，该选项将允许对象名称的“白名单”与应忽略哪些参数重新分配有关。

Answer 7

Following the documentation :

function (el) {
  const element = el
  element.expando = {}
}

Answer 8

An updated alternative if you don't really want to disable the rule, could be something like:

function (el) {
  Object.defineProperty(el, 'expando',{
    value: {},
    writable: true,
    configurable: true,
    enumerable: true
  });
}

Reference : https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty

Answer 9

You can also use lodash assignIn which mutates the object. assignIn(obj, { someNewObj });

https://lodash.com/docs/4.17.2#assignIn

Answer 10

You can use methods for updating data. Eg. "res.status(404)" instead of "res.statusCode = 404" I found the solution. https://github.com/eslint/eslint/issues/6505#issuecomment-282325903

/*eslint no-param-reassign: ["error", { "props": true, "ignorePropertyModificationsFor": ["$scope"] }]*/

app.controller('MyCtrl', function($scope) {
  $scope.something = true;
});

Answer 11

Based on the documentation at eslint ( https://eslint.org/docs/2.0.0/rules/no-param-reassign ), I solved it using the below written configuration in the .eslintrc.js file.

rules: {
  "no-param-reassign": [2, {"props": false}]
},

Answer 12

You can use:

(param) => {
  const data = Object.assign({}, param);
  data.element = 'some value';
}