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eb39fafa DC |
1 | /** |
2 | * @fileoverview A rule to disallow unnecessary `.call()` and `.apply()`. | |
3 | * @author Toru Nagashima | |
4 | */ | |
5 | ||
6 | "use strict"; | |
7 | ||
8 | const astUtils = require("./utils/ast-utils"); | |
9 | ||
10 | //------------------------------------------------------------------------------ | |
11 | // Helpers | |
12 | //------------------------------------------------------------------------------ | |
13 | ||
14 | /** | |
15 | * Checks whether or not a node is a `.call()`/`.apply()`. | |
16 | * @param {ASTNode} node A CallExpression node to check. | |
17 | * @returns {boolean} Whether or not the node is a `.call()`/`.apply()`. | |
18 | */ | |
19 | function isCallOrNonVariadicApply(node) { | |
6f036462 TL |
20 | const callee = astUtils.skipChainExpression(node.callee); |
21 | ||
eb39fafa | 22 | return ( |
6f036462 TL |
23 | callee.type === "MemberExpression" && |
24 | callee.property.type === "Identifier" && | |
25 | callee.computed === false && | |
eb39fafa | 26 | ( |
6f036462 TL |
27 | (callee.property.name === "call" && node.arguments.length >= 1) || |
28 | (callee.property.name === "apply" && node.arguments.length === 2 && node.arguments[1].type === "ArrayExpression") | |
eb39fafa DC |
29 | ) |
30 | ); | |
31 | } | |
32 | ||
33 | ||
34 | /** | |
35 | * Checks whether or not `thisArg` is not changed by `.call()`/`.apply()`. | |
36 | * @param {ASTNode|null} expectedThis The node that is the owner of the applied function. | |
37 | * @param {ASTNode} thisArg The node that is given to the first argument of the `.call()`/`.apply()`. | |
38 | * @param {SourceCode} sourceCode The ESLint source code object. | |
39 | * @returns {boolean} Whether or not `thisArg` is not changed by `.call()`/`.apply()`. | |
40 | */ | |
41 | function isValidThisArg(expectedThis, thisArg, sourceCode) { | |
42 | if (!expectedThis) { | |
43 | return astUtils.isNullOrUndefined(thisArg); | |
44 | } | |
45 | return astUtils.equalTokens(expectedThis, thisArg, sourceCode); | |
46 | } | |
47 | ||
48 | //------------------------------------------------------------------------------ | |
49 | // Rule Definition | |
50 | //------------------------------------------------------------------------------ | |
51 | ||
34eeec05 | 52 | /** @type {import('../shared/types').Rule} */ |
eb39fafa DC |
53 | module.exports = { |
54 | meta: { | |
55 | type: "suggestion", | |
56 | ||
57 | docs: { | |
8f9d1d4d | 58 | description: "Disallow unnecessary calls to `.call()` and `.apply()`", |
eb39fafa DC |
59 | recommended: false, |
60 | url: "https://eslint.org/docs/rules/no-useless-call" | |
61 | }, | |
62 | ||
63 | schema: [], | |
64 | ||
65 | messages: { | |
66 | unnecessaryCall: "Unnecessary '.{{name}}()'." | |
67 | } | |
68 | }, | |
69 | ||
70 | create(context) { | |
71 | const sourceCode = context.getSourceCode(); | |
72 | ||
73 | return { | |
74 | CallExpression(node) { | |
75 | if (!isCallOrNonVariadicApply(node)) { | |
76 | return; | |
77 | } | |
78 | ||
6f036462 TL |
79 | const callee = astUtils.skipChainExpression(node.callee); |
80 | const applied = astUtils.skipChainExpression(callee.object); | |
eb39fafa DC |
81 | const expectedThis = (applied.type === "MemberExpression") ? applied.object : null; |
82 | const thisArg = node.arguments[0]; | |
83 | ||
84 | if (isValidThisArg(expectedThis, thisArg, sourceCode)) { | |
6f036462 | 85 | context.report({ node, messageId: "unnecessaryCall", data: { name: callee.property.name } }); |
eb39fafa DC |
86 | } |
87 | } | |
88 | }; | |
89 | } | |
90 | }; |