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) {
20 const callee = astUtils.skipChainExpression(node.callee);
23 callee.type === "MemberExpression" &&
24 callee.property.type === "Identifier" &&
25 callee.computed === false &&
27 (callee.property.name === "call" && node.arguments.length >= 1) ||
28 (callee.property.name === "apply" && node.arguments.length === 2 && node.arguments[1].type === "ArrayExpression")
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()`.
41 function isValidThisArg(expectedThis, thisArg, sourceCode) {
43 return astUtils.isNullOrUndefined(thisArg);
45 return astUtils.equalTokens(expectedThis, thisArg, sourceCode);
48 //------------------------------------------------------------------------------
50 //------------------------------------------------------------------------------
57 description: "disallow unnecessary calls to `.call()` and `.apply()`",
58 category: "Best Practices",
60 url: "https://eslint.org/docs/rules/no-useless-call"
66 unnecessaryCall: "Unnecessary '.{{name}}()'."
71 const sourceCode = context.getSourceCode();
74 CallExpression(node) {
75 if (!isCallOrNonVariadicApply(node)) {
79 const callee = astUtils.skipChainExpression(node.callee);
80 const applied = astUtils.skipChainExpression(callee.object);
81 const expectedThis = (applied.type === "MemberExpression") ? applied.object : null;
82 const thisArg = node.arguments[0];
84 if (isValidThisArg(expectedThis, thisArg, sourceCode)) {
85 context.report({ node, messageId: "unnecessaryCall", data: { name: callee.property.name } });