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Commit 0fbd30e

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feat: Add prefer-array-from rule. Fixes #3 
1 parent 9e93e54 commit 0fbd30e

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8 files changed

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‎README.md‎

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Rules for Array functions and methods.
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## Contents
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- [Installation](#Installation)
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- [Rules](#Rules)
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- [`from-map`](#from-map)
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- [Examples](#Examples)
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- [`no-unnecessary-this-arg`](#no-unnecessary-this-arg)
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- [Checked Functions](#checked-functions)
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- [Checked Methods](#checked-methods)
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- [Examples](#Examples2)
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- [`prefer-array-from`](#prefer-array-from)
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- [Examples](#Examples3)
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- [`array-func/recommended` Configuration](#array-func-recommended-configuration)
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- [Using the Configuration](#using-the-configuration)
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- [License](#License)
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## Installation
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Install [ESLint](https://www.github.com/eslint/eslint) either locally or globally.
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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.
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#### Checked functions
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#### Checked Functions
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- `from` (fixable)
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#### Checked methods
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#### Checked Methods
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- `every`
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- `filter`
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- `find`
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array.filter(this.isGood, this);
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```
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### `prefer-array-from`
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Use `Array.from` instead of `[...iterable]` for performance benefits.
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This rule is auto fixable.
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#### Examples
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Code that triggers this rule:
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```js
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const iterable = [..."string"];
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const arrayCopy = [...iterable];
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```
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Code that doesn't trigger this rule:
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```js
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const array = [1, 2, 3];
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const extendedArray = [0, ...array];
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const arrayCopy = Array.from(array);
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const characterArray = Array.from("string");
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```
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## `array-func/recommended` Configuration
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The recommended configuration will set your parser ECMA Version to 2015, since that's when the Array functions and methods were added.
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Rule | Error level
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---- | -----------
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`from-map` | Error
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`no-unnecessary-this-arg` | Error
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Rule | Error level | Fixable
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---- | ----------- | -------
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`from-map` | Error | Yes
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`no-unnecessary-this-arg` | Error | Sometimes
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`prefer-array-from` | Error | Yes
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### Using the configuration
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### Using the Configuration
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To enable this configuration use the `extends` property in your `.eslintrc.json` config file (may look different for other config file styles):
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```json
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{

‎index.js‎

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module.exports = {
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rules: {
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"from-map": require("./rules/from-map"),
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"no-unnecessary-this-arg": require("./rules/no-unnecessary-this-arg")
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"no-unnecessary-this-arg": require("./rules/no-unnecessary-this-arg"),
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"prefer-array-from": require("./rules/prefer-array-from")
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},
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configs: {
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recommended: {
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plugins: [ 'array-func' ],
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rules: {
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"array-func/from-map": "error",
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"array-func/no-unnecessary-this-arg": "error"
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"array-func/no-unnecessary-this-arg": "error",
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"array-func/prefer-array-from": "error"
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}
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}
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}

‎lib/helpers/call-expression.js‎

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/**
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* @author Martin Giger
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* @license MIT
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*/
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"use strict";
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const {
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MEMBER_EXPRESSION,
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IDENTIFIER
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} = require("../type");
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// Helper functions for call expression nodes.
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exports.isMethod = (node, name) => "callee" in node && node.callee.type === MEMBER_EXPRESSION && node.callee.property.name === name;
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exports.getParent = (node) => node.callee.object;
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exports.isOnObject = (node, name) => "object" in node.callee && node.callee.object.type === IDENTIFIER && node.callee.object.name === name;

‎lib/type.js‎

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/**
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* @author Martin Giger
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* @license MIT
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*/
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"use strict";
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exports.MEMBER_EXPRESSION = "MemberExpression";
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exports.ARROW_FUNCTION_EXPRESSION = "ArrowFunctionExpression";
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exports.IDENTIFIER = "Identifier";
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exports.SPREAD_ELEMENT = "SpreadElement";

‎rules/prefer-array-from.js‎

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/**
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* @author Martin Giger
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* @license MIT
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*/
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"use strict";
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const { SPREAD_ELEMENT } = require("../lib/type");
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const SINGLE_ELEMENT = 1,
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firstElement = (arr) => {
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const [ el ] = arr;
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return el;
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};
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module.exports = {
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meta: {
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docs: {
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description: "Prefer using Array.from over spreading an interable in an array literal.",
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recommended: true
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},
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schema: [],
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fixable: "code"
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},
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create(context) {
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return {
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"ArrayExpression:exit"(node) {
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if(node.elements.length !== SINGLE_ELEMENT || firstElement(node.elements).type !== SPREAD_ELEMENT) {
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return;
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}
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context.report({
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node,
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loc: node.loc,
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message: "Use Array.from to convert from iterable to array",
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fix(fixer) {
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const sourceCode = context.getSourceCode();
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return fixer.replaceText(node, `Array.from(${sourceCode.getText(firstElement(node.elements).argument)})`);
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}
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});
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}
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};
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}
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};

‎test/helpers-call-expression.js‎

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import test from 'ava';
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import { isMethod, getParent, isOnObject } from '../lib/helpers/call-expression';
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import { MEMBER_EXPRESSION, IDENTIFIER } from '../lib/type';
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test('is method', (t) => {
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const name = "test";
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t.true(isMethod({
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callee: {
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type: MEMBER_EXPRESSION,
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property: {
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name
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}
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}
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}, name));
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});
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test('not is method', (t) => {
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const name = 'test';
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t.false(isMethod({}, name));
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t.false(isMethod({
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callee: {
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type: IDENTIFIER,
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property: {
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name
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}
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}
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}, name));
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t.false(isMethod({
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callee: {
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type: MEMBER_EXPRESSION,
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property: {
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name: 'foo'
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}
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}
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}));
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});
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test('get parent', (t) => {
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const parent = 'foo';
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t.is(getParent({
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callee: {
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object: parent
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}
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}), parent);
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});
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test('is on object', (t) => {
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const name = 'test';
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t.true(isOnObject({
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callee: {
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object: {
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type: IDENTIFIER,
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name
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}
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}
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}, name));
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});
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test('is not on object', (t) => {
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const name = 'test';
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t.false(isOnObject({
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callee: {}
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}, name));
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t.false(isOnObject({
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callee: {
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type: MEMBER_EXPRESSION,
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name
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}
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}, name));
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t.false(isOnObject({
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callee: {
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type: IDENTIFIER,
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name: 'foo'
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}
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}, name));
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});

‎test/rules/prefer-array-from.js‎

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import test from 'ava';
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import AvaRuleTester from 'eslint-ava-rule-tester';
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import rule from '../../rules/prefer-array-from';
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const ruleTester = new AvaRuleTester(test, {
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parserOptions: {
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ecmaVersion: 2015
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}
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});
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const message = "Use Array.from to convert from iterable to array";
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ruleTester.run('from-map', rule, {
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valid: [
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'Array.from(new Set())',
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'Array.from(iterable)',
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'[1, ...iterable]',
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'[1, 2, 3]',
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'[iterable]'
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],
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invalid: [
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{
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code: '[...iterable]',
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errors: [ {
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message,
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column: 1,
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line: 1
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} ],
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output: 'Array.from(iterable)'
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},
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{
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code: '[...[1, 2]]',
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errors: [ {
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message,
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column: 1,
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line: 1
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} ],
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output: 'Array.from([1, 2])'
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},
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{
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code: '[..."test"]',
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errors: [ {
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message,
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column: 1,
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line: 1
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} ],
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output: 'Array.from("test")'
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}
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]
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});

‎test/type.js‎

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import test from 'ava';
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import {
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SPREAD_ELEMENT,
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ARROW_FUNCTION_EXPRESSION,
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MEMBER_EXPRESSION,
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IDENTIFIER
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} from '../lib/type';
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test('Spread element', (t) => {
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t.is(SPREAD_ELEMENT, "SpreadElement");
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});
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test('Arrow function expression', (t) => {
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t.is(ARROW_FUNCTION_EXPRESSION, "ArrowFunctionExpression");
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});
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test('Member expression', (t) => {
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t.is(MEMBER_EXPRESSION, "MemberExpression");
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});
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test('Identifier', (t) => {
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t.is(IDENTIFIER, "Identifier");
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});

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