/** * @fileoverview A rule to disallow unnecessary `.call()` and `.apply()`. * @author Toru Nagashima */ "use strict"; const astUtils = require("../ast-utils"); //------------------------------------------------------------------------------ // Helpers //------------------------------------------------------------------------------ /** * Checks whether or not a node is a `.call()`/`.apply()`. * @param {ASTNode} node - A CallExpression node to check. * @returns {boolean} Whether or not the node is a `.call()`/`.apply()`. */ function isCallOrNonVariadicApply(node) { return ( node.callee.type === "MemberExpression" && node.callee.property.type === "Identifier" && node.callee.computed === false && ( (node.callee.property.name === "call" && node.arguments.length >= 1) || (node.callee.property.name === "apply" && node.arguments.length === 2 && node.arguments[1].type === "ArrayExpression") ) ); } /** * Checks whether or not `thisArg` is not changed by `.call()`/`.apply()`. * @param {ASTNode|null} expectedThis - The node that is the owner of the applied function. * @param {ASTNode} thisArg - The node that is given to the first argument of the `.call()`/`.apply()`. * @param {SourceCode} sourceCode - The ESLint source code object. * @returns {boolean} Whether or not `thisArg` is not changed by `.call()`/`.apply()`. */ function isValidThisArg(expectedThis, thisArg, sourceCode) { if (!expectedThis) { return astUtils.isNullOrUndefined(thisArg); } return astUtils.equalTokens(expectedThis, thisArg, sourceCode); } //------------------------------------------------------------------------------ // Rule Definition //------------------------------------------------------------------------------ module.exports = { meta: { docs: { description: "disallow unnecessary calls to `.call()` and `.apply()`", category: "Best Practices", recommended: false }, schema: [] }, create(context) { const sourceCode = context.getSourceCode(); return { CallExpression(node) { if (!isCallOrNonVariadicApply(node)) { return; } const applied = node.callee.object; const expectedThis = (applied.type === "MemberExpression") ? applied.object : null; const thisArg = node.arguments[0]; if (isValidThisArg(expectedThis, thisArg, sourceCode)) { context.report({ node, message: "unnecessary '.{{name}}()'.", data: { name: node.callee.property.name } }); } } }; } };