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/**
* @fileoverview Rule to flag unnecessary bind calls
* @author Bence Dányi <bence@danyi.me>
*/
"use strict";
//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------
const astUtils = require("../ast-utils");
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
module.exports = {
meta: {
docs: {
description: "disallow unnecessary calls to `.bind()`",
category: "Best Practices",
recommended: false
},
schema: [],
fixable: "code"
},
create(context) {
let scopeInfo = null;
/**
* Reports a given function node.
*
* @param {ASTNode} node - A node to report. This is a FunctionExpression or
* an ArrowFunctionExpression.
* @returns {void}
*/
function report(node) {
context.report({
node: node.parent.parent,
message: "The function binding is unnecessary.",
loc: node.parent.property.loc.start,
fix(fixer) {
const firstTokenToRemove = context.getSourceCode()
.getFirstTokenBetween(node.parent.object, node.parent.property, astUtils.isNotClosingParenToken);
return fixer.removeRange([firstTokenToRemove.range[0], node.parent.parent.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) {
const parent = node.parent;
const grandparent = parent.parent;
return (
grandparent &&
grandparent.type === "CallExpression" &&
grandparent.callee === parent &&
grandparent.arguments.length === 1 &&
parent.type === "MemberExpression" &&
parent.object === node &&
astUtils.getStaticPropertyName(parent) === "bind"
);
}
/**
* 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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