2 * @fileoverview A rule to disallow unnecessary `.call()` and `.apply()`.
3 * @author Toru Nagashima
8 const astUtils = require("./utils/ast-utils");
10 //------------------------------------------------------------------------------
12 //------------------------------------------------------------------------------
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()`.
19 function isCallOrNonVariadicApply(node) {
21 node.callee.type === "MemberExpression" &&
22 node.callee.property.type === "Identifier" &&
23 node.callee.computed === false &&
25 (node.callee.property.name === "call" && node.arguments.length >= 1) ||
26 (node.callee.property.name === "apply" && node.arguments.length === 2 && node.arguments[1].type === "ArrayExpression")
33 * Checks whether or not `thisArg` is not changed by `.call()`/`.apply()`.
34 * @param {ASTNode|null} expectedThis The node that is the owner of the applied function.
35 * @param {ASTNode} thisArg The node that is given to the first argument of the `.call()`/`.apply()`.
36 * @param {SourceCode} sourceCode The ESLint source code object.
37 * @returns {boolean} Whether or not `thisArg` is not changed by `.call()`/`.apply()`.
39 function isValidThisArg(expectedThis, thisArg, sourceCode) {
41 return astUtils.isNullOrUndefined(thisArg);
43 return astUtils.equalTokens(expectedThis, thisArg, sourceCode);
46 //------------------------------------------------------------------------------
48 //------------------------------------------------------------------------------
55 description: "disallow unnecessary calls to `.call()` and `.apply()`",
56 category: "Best Practices",
58 url: "https://eslint.org/docs/rules/no-useless-call"
65 const sourceCode = context.getSourceCode();
68 CallExpression(node) {
69 if (!isCallOrNonVariadicApply(node)) {
73 const applied = node.callee.object;
74 const expectedThis = (applied.type === "MemberExpression") ? applied.object : null;
75 const thisArg = node.arguments[0];
77 if (isValidThisArg(expectedThis, thisArg, sourceCode)) {
78 context.report({ node, message: "unnecessary '.{{name}}()'.", data: { name: node.callee.property.name } });