no-unnecessary-this-arg

Avoid the this parameter when providing arrow function as callback in array functions.

The this parameter is useless when providing arrow functions, since the this of arrow functions can not be rebound, thus the parameter has no effect.

The fix is usually to omit the parameter. The Array methods can't be auto-fixed, since the detection of array methods is not confident enough to know that the method is being called on an array.

Checked Functions

• from (fixable)

Checked Methods

• every
• filter
• find
• findIndex
• forEach
• map
• some

Examples

Code that triggers this rule:

const array = Array.from("example", (char) => char.charCodeAt(0), this);

const e = array.find((char) => char === 101, this);

const exampleAsArray = array.map((char) => String.fromCharCode(char), this);

const eIndex = array.findIndex((char) => char === 101, this);

const containsE = array.some((char) => char === 101, this);

const isOnlyE = array.every((char) => char === 101, this);

const onlyEs = array.filter((char) => char === 101, this);

array.forEach((char) => console.log(char), this);

Code that doesn't trigger this rule:

const array = Array.from("example", (char) => char.charCodeAt(0));
const alternateArray = Array.from("example", function(char) {
    return char.charCodeAt(this)
}, 0);

const e = array.find((char) => char === 101);

const exampleAsArray = array.map((char) => String.fromCharCode(char));

const eIndex = array.findIndex((char) => char === 101);

const containsE = array.some((char) => char === 101);

const isOnlyE = array.every((char) => char === 101);

const onlyEs = array.filter(function(char) {
    return char === this
}, 101);

array.forEach(function(char) {
    this.log(char);
}, console);

array.filter(this.isGood, this);

Using the rule

To use this rule, your eslint.config.js should at least contain the following:

import arrayFunc from "eslint-plugin-array-func";

export default [
  {
    plugins: {
      "array-func": arrayFunc
    },
    rules: {
      "array-func/no-unnecessary-this-arg": "error"
    }
  }
];