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Luca Schwan
310
node_modules/eslint/lib/rules/prefer-arrow-callback.js
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310
node_modules/eslint/lib/rules/prefer-arrow-callback.js
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/**
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* @fileoverview A rule to suggest using arrow functions as callbacks.
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* @author Toru Nagashima
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*/
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"use strict";
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//------------------------------------------------------------------------------
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// Helpers
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//------------------------------------------------------------------------------
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/**
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* Checks whether or not a given variable is a function name.
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* @param {eslint-scope.Variable} variable A variable to check.
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* @returns {boolean} `true` if the variable is a function name.
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*/
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function isFunctionName(variable) {
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return variable && variable.defs[0].type === "FunctionName";
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}
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/**
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* Checks whether or not a given MetaProperty node equals to a given value.
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* @param {ASTNode} node A MetaProperty node to check.
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* @param {string} metaName The name of `MetaProperty.meta`.
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* @param {string} propertyName The name of `MetaProperty.property`.
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* @returns {boolean} `true` if the node is the specific value.
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*/
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function checkMetaProperty(node, metaName, propertyName) {
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return node.meta.name === metaName && node.property.name === propertyName;
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}
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/**
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* Gets the variable object of `arguments` which is defined implicitly.
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* @param {eslint-scope.Scope} scope A scope to get.
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* @returns {eslint-scope.Variable} The found variable object.
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*/
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function getVariableOfArguments(scope) {
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const variables = scope.variables;
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for (let i = 0; i < variables.length; ++i) {
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const variable = variables[i];
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if (variable.name === "arguments") {
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/*
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* If there was a parameter which is named "arguments", the
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* implicit "arguments" is not defined.
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* So does fast return with null.
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*/
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return (variable.identifiers.length === 0) ? variable : null;
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}
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}
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/* istanbul ignore next */
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return null;
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}
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/**
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* Checkes whether or not a given node is a callback.
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* @param {ASTNode} node A node to check.
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* @returns {Object}
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* {boolean} retv.isCallback - `true` if the node is a callback.
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* {boolean} retv.isLexicalThis - `true` if the node is with `.bind(this)`.
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*/
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function getCallbackInfo(node) {
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const retv = { isCallback: false, isLexicalThis: false };
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let currentNode = node;
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let parent = node.parent;
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while (currentNode) {
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switch (parent.type) {
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// Checks parents recursively.
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case "LogicalExpression":
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case "ConditionalExpression":
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break;
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// Checks whether the parent node is `.bind(this)` call.
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case "MemberExpression":
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if (parent.object === currentNode &&
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!parent.property.computed &&
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parent.property.type === "Identifier" &&
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parent.property.name === "bind" &&
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parent.parent.type === "CallExpression" &&
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parent.parent.callee === parent
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) {
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retv.isLexicalThis = (
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parent.parent.arguments.length === 1 &&
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parent.parent.arguments[0].type === "ThisExpression"
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);
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parent = parent.parent;
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} else {
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return retv;
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}
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break;
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// Checks whether the node is a callback.
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case "CallExpression":
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case "NewExpression":
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if (parent.callee !== currentNode) {
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retv.isCallback = true;
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}
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return retv;
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default:
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return retv;
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}
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currentNode = parent;
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parent = parent.parent;
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}
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/* istanbul ignore next */
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throw new Error("unreachable");
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}
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/**
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* Checks whether a simple list of parameters contains any duplicates. This does not handle complex
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* parameter lists (e.g. with destructuring), since complex parameter lists are a SyntaxError with duplicate
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* parameter names anyway. Instead, it always returns `false` for complex parameter lists.
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* @param {ASTNode[]} paramsList The list of parameters for a function
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* @returns {boolean} `true` if the list of parameters contains any duplicates
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*/
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function hasDuplicateParams(paramsList) {
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return paramsList.every(param => param.type === "Identifier") && paramsList.length !== new Set(paramsList.map(param => param.name)).size;
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}
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//------------------------------------------------------------------------------
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// Rule Definition
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//------------------------------------------------------------------------------
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module.exports = {
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meta: {
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type: "suggestion",
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docs: {
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description: "require using arrow functions for callbacks",
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category: "ECMAScript 6",
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recommended: false,
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url: "https://eslint.org/docs/rules/prefer-arrow-callback"
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},
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schema: [
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{
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type: "object",
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properties: {
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allowNamedFunctions: {
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type: "boolean",
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default: false
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},
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allowUnboundThis: {
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type: "boolean",
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default: true
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}
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},
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additionalProperties: false
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}
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],
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fixable: "code"
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},
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create(context) {
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const options = context.options[0] || {};
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const allowUnboundThis = options.allowUnboundThis !== false; // default to true
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const allowNamedFunctions = options.allowNamedFunctions;
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const sourceCode = context.getSourceCode();
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/*
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* {Array<{this: boolean, super: boolean, meta: boolean}>}
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* - this - A flag which shows there are one or more ThisExpression.
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* - super - A flag which shows there are one or more Super.
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* - meta - A flag which shows there are one or more MethProperty.
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*/
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let stack = [];
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/**
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* Pushes new function scope with all `false` flags.
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* @returns {void}
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*/
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function enterScope() {
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stack.push({ this: false, super: false, meta: false });
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}
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/**
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* Pops a function scope from the stack.
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* @returns {{this: boolean, super: boolean, meta: boolean}} The information of the last scope.
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*/
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function exitScope() {
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return stack.pop();
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}
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return {
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// Reset internal state.
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Program() {
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stack = [];
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},
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// If there are below, it cannot replace with arrow functions merely.
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ThisExpression() {
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const info = stack[stack.length - 1];
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if (info) {
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info.this = true;
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}
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},
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Super() {
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const info = stack[stack.length - 1];
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if (info) {
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info.super = true;
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}
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},
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MetaProperty(node) {
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const info = stack[stack.length - 1];
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if (info && checkMetaProperty(node, "new", "target")) {
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info.meta = true;
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}
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},
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// To skip nested scopes.
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FunctionDeclaration: enterScope,
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"FunctionDeclaration:exit": exitScope,
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// Main.
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FunctionExpression: enterScope,
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"FunctionExpression:exit"(node) {
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const scopeInfo = exitScope();
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// Skip named function expressions
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if (allowNamedFunctions && node.id && node.id.name) {
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return;
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}
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// Skip generators.
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if (node.generator) {
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return;
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}
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// Skip recursive functions.
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const nameVar = context.getDeclaredVariables(node)[0];
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if (isFunctionName(nameVar) && nameVar.references.length > 0) {
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return;
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}
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// Skip if it's using arguments.
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const variable = getVariableOfArguments(context.getScope());
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if (variable && variable.references.length > 0) {
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return;
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}
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// Reports if it's a callback which can replace with arrows.
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const callbackInfo = getCallbackInfo(node);
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if (callbackInfo.isCallback &&
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(!allowUnboundThis || !scopeInfo.this || callbackInfo.isLexicalThis) &&
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!scopeInfo.super &&
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!scopeInfo.meta
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) {
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context.report({
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node,
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message: "Unexpected function expression.",
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fix(fixer) {
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if ((!callbackInfo.isLexicalThis && scopeInfo.this) || hasDuplicateParams(node.params)) {
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/*
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* If the callback function does not have .bind(this) and contains a reference to `this`, there
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* is no way to determine what `this` should be, so don't perform any fixes.
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* If the callback function has duplicates in its list of parameters (possible in sloppy mode),
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* don't replace it with an arrow function, because this is a SyntaxError with arrow functions.
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*/
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return null;
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}
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const paramsLeftParen = node.params.length ? sourceCode.getTokenBefore(node.params[0]) : sourceCode.getTokenBefore(node.body, 1);
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const paramsRightParen = sourceCode.getTokenBefore(node.body);
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const asyncKeyword = node.async ? "async " : "";
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const paramsFullText = sourceCode.text.slice(paramsLeftParen.range[0], paramsRightParen.range[1]);
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const arrowFunctionText = `${asyncKeyword}${paramsFullText} => ${sourceCode.getText(node.body)}`;
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/*
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* If the callback function has `.bind(this)`, replace it with an arrow function and remove the binding.
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* Otherwise, just replace the arrow function itself.
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*/
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const replacedNode = callbackInfo.isLexicalThis ? node.parent.parent : node;
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/*
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* If the replaced node is part of a BinaryExpression, LogicalExpression, or MemberExpression, then
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* the arrow function needs to be parenthesized, because `foo || () => {}` is invalid syntax even
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* though `foo || function() {}` is valid.
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*/
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const needsParens = replacedNode.parent.type !== "CallExpression" && replacedNode.parent.type !== "ConditionalExpression";
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const replacementText = needsParens ? `(${arrowFunctionText})` : arrowFunctionText;
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return fixer.replaceText(replacedNode, replacementText);
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}
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});
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}
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}
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};
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}
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};
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