--- /dev/null
+/**
+ * @fileoverview Rule to flag unnecessary bind calls
+ * @author Bence Dányi <bence@danyi.me>
+ */
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+const astUtils = require("./utils/ast-utils");
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+const SIDE_EFFECT_FREE_NODE_TYPES = new Set(["Literal", "Identifier", "ThisExpression", "FunctionExpression"]);
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+ meta: {
+ type: "suggestion",
+
+ docs: {
+ description: "disallow unnecessary calls to `.bind()`",
+ category: "Best Practices",
+ recommended: false,
+ url: "https://eslint.org/docs/rules/no-extra-bind"
+ },
+
+ schema: [],
+ fixable: "code",
+
+ messages: {
+ unexpected: "The function binding is unnecessary."
+ }
+ },
+
+ create(context) {
+ const sourceCode = context.getSourceCode();
+ let scopeInfo = null;
+
+ /**
+ * Checks if a node is free of side effects.
+ *
+ * This check is stricter than it needs to be, in order to keep the implementation simple.
+ * @param {ASTNode} node A node to check.
+ * @returns {boolean} True if the node is known to be side-effect free, false otherwise.
+ */
+ function isSideEffectFree(node) {
+ return SIDE_EFFECT_FREE_NODE_TYPES.has(node.type);
+ }
+
+ /**
+ * Reports a given function node.
+ * @param {ASTNode} node A node to report. This is a FunctionExpression or
+ * an ArrowFunctionExpression.
+ * @returns {void}
+ */
+ function report(node) {
+ const memberNode = node.parent;
+ const callNode = memberNode.parent.type === "ChainExpression"
+ ? memberNode.parent.parent
+ : memberNode.parent;
+
+ context.report({
+ node: callNode,
+ messageId: "unexpected",
+ loc: memberNode.property.loc,
+
+ fix(fixer) {
+ if (!isSideEffectFree(callNode.arguments[0])) {
+ return null;
+ }
+
+ /*
+ * The list of the first/last token pair of a removal range.
+ * This is two parts because closing parentheses may exist between the method name and arguments.
+ * E.g. `(function(){}.bind ) (obj)`
+ * ^^^^^ ^^^^^ < removal ranges
+ * E.g. `(function(){}?.['bind'] ) ?.(obj)`
+ * ^^^^^^^^^^ ^^^^^^^ < removal ranges
+ */
+ const tokenPairs = [
+ [
+
+ // `.`, `?.`, or `[` token.
+ sourceCode.getTokenAfter(
+ memberNode.object,
+ astUtils.isNotClosingParenToken
+ ),
+
+ // property name or `]` token.
+ sourceCode.getLastToken(memberNode)
+ ],
+ [
+
+ // `?.` or `(` token of arguments.
+ sourceCode.getTokenAfter(
+ memberNode,
+ astUtils.isNotClosingParenToken
+ ),
+
+ // `)` token of arguments.
+ sourceCode.getLastToken(callNode)
+ ]
+ ];
+ const firstTokenToRemove = tokenPairs[0][0];
+ const lastTokenToRemove = tokenPairs[1][1];
+
+ if (sourceCode.commentsExistBetween(firstTokenToRemove, lastTokenToRemove)) {
+ return null;
+ }
+
+ return tokenPairs.map(([start, end]) =>
+ fixer.removeRange([start.range[0], end.range[1]]));
+ }
+ });
+ }
+
+ /**
+ * Checks whether or not a given function node is the callee of `.bind()`
+ * method.
+ *
+ * e.g. `(function() {}.bind(foo))`
+ * @param {ASTNode} node A node to report. This is a FunctionExpression or
+ * an ArrowFunctionExpression.
+ * @returns {boolean} `true` if the node is the callee of `.bind()` method.
+ */
+ function isCalleeOfBindMethod(node) {
+ if (!astUtils.isSpecificMemberAccess(node.parent, null, "bind")) {
+ return false;
+ }
+
+ // The node of `*.bind` member access.
+ const bindNode = node.parent.parent.type === "ChainExpression"
+ ? node.parent.parent
+ : node.parent;
+
+ return (
+ bindNode.parent.type === "CallExpression" &&
+ bindNode.parent.callee === bindNode &&
+ bindNode.parent.arguments.length === 1 &&
+ bindNode.parent.arguments[0].type !== "SpreadElement"
+ );
+ }
+
+ /**
+ * Adds a scope information object to the stack.
+ * @param {ASTNode} node A node to add. This node is a FunctionExpression
+ * or a FunctionDeclaration node.
+ * @returns {void}
+ */
+ function enterFunction(node) {
+ scopeInfo = {
+ isBound: isCalleeOfBindMethod(node),
+ thisFound: false,
+ upper: scopeInfo
+ };
+ }
+
+ /**
+ * Removes the scope information object from the top of the stack.
+ * At the same time, this reports the function node if the function has
+ * `.bind()` and the `this` keywords found.
+ * @param {ASTNode} node A node to remove. This node is a
+ * FunctionExpression or a FunctionDeclaration node.
+ * @returns {void}
+ */
+ function exitFunction(node) {
+ if (scopeInfo.isBound && !scopeInfo.thisFound) {
+ report(node);
+ }
+
+ scopeInfo = scopeInfo.upper;
+ }
+
+ /**
+ * Reports a given arrow function if the function is callee of `.bind()`
+ * method.
+ * @param {ASTNode} node A node to report. This node is an
+ * ArrowFunctionExpression.
+ * @returns {void}
+ */
+ function exitArrowFunction(node) {
+ if (isCalleeOfBindMethod(node)) {
+ report(node);
+ }
+ }
+
+ /**
+ * Set the mark as the `this` keyword was found in this scope.
+ * @returns {void}
+ */
+ function markAsThisFound() {
+ if (scopeInfo) {
+ scopeInfo.thisFound = true;
+ }
+ }
+
+ return {
+ "ArrowFunctionExpression:exit": exitArrowFunction,
+ FunctionDeclaration: enterFunction,
+ "FunctionDeclaration:exit": exitFunction,
+ FunctionExpression: enterFunction,
+ "FunctionExpression:exit": exitFunction,
+ ThisExpression: markAsThisFound
+ };
+ }
+};
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