Current File : /var/www/html/node_modules/eslint/lib/rules/prefer-arrow-callback.js
/**
* @fileoverview A rule to suggest using arrow functions as callbacks.
* @author Toru Nagashima
*/
"use strict";
const astUtils = require("./utils/ast-utils");
//------------------------------------------------------------------------------
// Helpers
//------------------------------------------------------------------------------
/**
* Checks whether or not a given variable is a function name.
* @param {eslint-scope.Variable} variable A variable to check.
* @returns {boolean} `true` if the variable is a function name.
*/
function isFunctionName(variable) {
return variable && variable.defs[0].type === "FunctionName";
}
/**
* Checks whether or not a given MetaProperty node equals to a given value.
* @param {ASTNode} node A MetaProperty node to check.
* @param {string} metaName The name of `MetaProperty.meta`.
* @param {string} propertyName The name of `MetaProperty.property`.
* @returns {boolean} `true` if the node is the specific value.
*/
function checkMetaProperty(node, metaName, propertyName) {
return node.meta.name === metaName && node.property.name === propertyName;
}
/**
* Gets the variable object of `arguments` which is defined implicitly.
* @param {eslint-scope.Scope} scope A scope to get.
* @returns {eslint-scope.Variable} The found variable object.
*/
function getVariableOfArguments(scope) {
const variables = scope.variables;
for (let i = 0; i < variables.length; ++i) {
const variable = variables[i];
if (variable.name === "arguments") {
/*
* If there was a parameter which is named "arguments", the
* implicit "arguments" is not defined.
* So does fast return with null.
*/
return (variable.identifiers.length === 0) ? variable : null;
}
}
/* istanbul ignore next */
return null;
}
/**
* Checks whether or not a given node is a callback.
* @param {ASTNode} node A node to check.
* @throws {Error} (Unreachable.)
* @returns {Object}
* {boolean} retv.isCallback - `true` if the node is a callback.
* {boolean} retv.isLexicalThis - `true` if the node is with `.bind(this)`.
*/
function getCallbackInfo(node) {
const retv = { isCallback: false, isLexicalThis: false };
let currentNode = node;
let parent = node.parent;
let bound = false;
while (currentNode) {
switch (parent.type) {
// Checks parents recursively.
case "LogicalExpression":
case "ChainExpression":
case "ConditionalExpression":
break;
// Checks whether the parent node is `.bind(this)` call.
case "MemberExpression":
if (
parent.object === currentNode &&
!parent.property.computed &&
parent.property.type === "Identifier" &&
parent.property.name === "bind"
) {
const maybeCallee = parent.parent.type === "ChainExpression"
? parent.parent
: parent;
if (astUtils.isCallee(maybeCallee)) {
if (!bound) {
bound = true; // Use only the first `.bind()` to make `isLexicalThis` value.
retv.isLexicalThis = (
maybeCallee.parent.arguments.length === 1 &&
maybeCallee.parent.arguments[0].type === "ThisExpression"
);
}
parent = maybeCallee.parent;
} else {
return retv;
}
} else {
return retv;
}
break;
// Checks whether the node is a callback.
case "CallExpression":
case "NewExpression":
if (parent.callee !== currentNode) {
retv.isCallback = true;
}
return retv;
default:
return retv;
}
currentNode = parent;
parent = parent.parent;
}
/* istanbul ignore next */
throw new Error("unreachable");
}
/**
* Checks whether a simple list of parameters contains any duplicates. This does not handle complex
* parameter lists (e.g. with destructuring), since complex parameter lists are a SyntaxError with duplicate
* parameter names anyway. Instead, it always returns `false` for complex parameter lists.
* @param {ASTNode[]} paramsList The list of parameters for a function
* @returns {boolean} `true` if the list of parameters contains any duplicates
*/
function hasDuplicateParams(paramsList) {
return paramsList.every(param => param.type === "Identifier") && paramsList.length !== new Set(paramsList.map(param => param.name)).size;
}
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
/** @type {import('../shared/types').Rule} */
module.exports = {
meta: {
type: "suggestion",
docs: {
description: "require using arrow functions for callbacks",
recommended: false,
url: "https://eslint.org/docs/rules/prefer-arrow-callback"
},
schema: [
{
type: "object",
properties: {
allowNamedFunctions: {
type: "boolean",
default: false
},
allowUnboundThis: {
type: "boolean",
default: true
}
},
additionalProperties: false
}
],
fixable: "code",
messages: {
preferArrowCallback: "Unexpected function expression."
}
},
create(context) {
const options = context.options[0] || {};
const allowUnboundThis = options.allowUnboundThis !== false; // default to true
const allowNamedFunctions = options.allowNamedFunctions;
const sourceCode = context.getSourceCode();
/*
* {Array<{this: boolean, super: boolean, meta: boolean}>}
* - this - A flag which shows there are one or more ThisExpression.
* - super - A flag which shows there are one or more Super.
* - meta - A flag which shows there are one or more MethProperty.
*/
let stack = [];
/**
* Pushes new function scope with all `false` flags.
* @returns {void}
*/
function enterScope() {
stack.push({ this: false, super: false, meta: false });
}
/**
* Pops a function scope from the stack.
* @returns {{this: boolean, super: boolean, meta: boolean}} The information of the last scope.
*/
function exitScope() {
return stack.pop();
}
return {
// Reset internal state.
Program() {
stack = [];
},
// If there are below, it cannot replace with arrow functions merely.
ThisExpression() {
const info = stack[stack.length - 1];
if (info) {
info.this = true;
}
},
Super() {
const info = stack[stack.length - 1];
if (info) {
info.super = true;
}
},
MetaProperty(node) {
const info = stack[stack.length - 1];
if (info && checkMetaProperty(node, "new", "target")) {
info.meta = true;
}
},
// To skip nested scopes.
FunctionDeclaration: enterScope,
"FunctionDeclaration:exit": exitScope,
// Main.
FunctionExpression: enterScope,
"FunctionExpression:exit"(node) {
const scopeInfo = exitScope();
// Skip named function expressions
if (allowNamedFunctions && node.id && node.id.name) {
return;
}
// Skip generators.
if (node.generator) {
return;
}
// Skip recursive functions.
const nameVar = context.getDeclaredVariables(node)[0];
if (isFunctionName(nameVar) && nameVar.references.length > 0) {
return;
}
// Skip if it's using arguments.
const variable = getVariableOfArguments(context.getScope());
if (variable && variable.references.length > 0) {
return;
}
// Reports if it's a callback which can replace with arrows.
const callbackInfo = getCallbackInfo(node);
if (callbackInfo.isCallback &&
(!allowUnboundThis || !scopeInfo.this || callbackInfo.isLexicalThis) &&
!scopeInfo.super &&
!scopeInfo.meta
) {
context.report({
node,
messageId: "preferArrowCallback",
*fix(fixer) {
if ((!callbackInfo.isLexicalThis && scopeInfo.this) || hasDuplicateParams(node.params)) {
/*
* If the callback function does not have .bind(this) and contains a reference to `this`, there
* is no way to determine what `this` should be, so don't perform any fixes.
* If the callback function has duplicates in its list of parameters (possible in sloppy mode),
* don't replace it with an arrow function, because this is a SyntaxError with arrow functions.
*/
return;
}
// Remove `.bind(this)` if exists.
if (callbackInfo.isLexicalThis) {
const memberNode = node.parent;
/*
* If `.bind(this)` exists but the parent is not `.bind(this)`, don't remove it automatically.
* E.g. `(foo || function(){}).bind(this)`
*/
if (memberNode.type !== "MemberExpression") {
return;
}
const callNode = memberNode.parent;
const firstTokenToRemove = sourceCode.getTokenAfter(memberNode.object, astUtils.isNotClosingParenToken);
const lastTokenToRemove = sourceCode.getLastToken(callNode);
/*
* If the member expression is parenthesized, don't remove the right paren.
* E.g. `(function(){}.bind)(this)`
* ^^^^^^^^^^^^
*/
if (astUtils.isParenthesised(sourceCode, memberNode)) {
return;
}
// If comments exist in the `.bind(this)`, don't remove those.
if (sourceCode.commentsExistBetween(firstTokenToRemove, lastTokenToRemove)) {
return;
}
yield fixer.removeRange([firstTokenToRemove.range[0], lastTokenToRemove.range[1]]);
}
// Convert the function expression to an arrow function.
const functionToken = sourceCode.getFirstToken(node, node.async ? 1 : 0);
const leftParenToken = sourceCode.getTokenAfter(functionToken, astUtils.isOpeningParenToken);
if (sourceCode.commentsExistBetween(functionToken, leftParenToken)) {
// Remove only extra tokens to keep comments.
yield fixer.remove(functionToken);
if (node.id) {
yield fixer.remove(node.id);
}
} else {
// Remove extra tokens and spaces.
yield fixer.removeRange([functionToken.range[0], leftParenToken.range[0]]);
}
yield fixer.insertTextBefore(node.body, "=> ");
// Get the node that will become the new arrow function.
let replacedNode = callbackInfo.isLexicalThis ? node.parent.parent : node;
if (replacedNode.type === "ChainExpression") {
replacedNode = replacedNode.parent;
}
/*
* If the replaced node is part of a BinaryExpression, LogicalExpression, or MemberExpression, then
* the arrow function needs to be parenthesized, because `foo || () => {}` is invalid syntax even
* though `foo || function() {}` is valid.
*/
if (
replacedNode.parent.type !== "CallExpression" &&
replacedNode.parent.type !== "ConditionalExpression" &&
!astUtils.isParenthesised(sourceCode, replacedNode) &&
!astUtils.isParenthesised(sourceCode, node)
) {
yield fixer.insertTextBefore(replacedNode, "(");
yield fixer.insertTextAfter(replacedNode, ")");
}
}
});
}
}
};
}
};
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