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/**
* @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,
url: "https://eslint.org/docs/rules/no-useless-call"
},
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 } });
}
}
};
}
};
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