no-self-compare.js
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/**
* @fileoverview Rule to flag comparison where left part is the same as the right
* part.
* @author Ilya Volodin
*/
"use strict";
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
/** @type {import('../shared/types').Rule} */
module.exports = {
meta: {
type: "problem",
docs: {
description: "Disallow comparisons where both sides are exactly the same",
recommended: false,
url: "https://eslint.org/docs/rules/no-self-compare"
},
schema: [],
messages: {
comparingToSelf: "Comparing to itself is potentially pointless."
}
},
create(context) {
const sourceCode = context.getSourceCode();
/**
* Determines whether two nodes are composed of the same tokens.
* @param {ASTNode} nodeA The first node
* @param {ASTNode} nodeB The second node
* @returns {boolean} true if the nodes have identical token representations
*/
function hasSameTokens(nodeA, nodeB) {
const tokensA = sourceCode.getTokens(nodeA);
const tokensB = sourceCode.getTokens(nodeB);
return tokensA.length === tokensB.length &&
tokensA.every((token, index) => token.type === tokensB[index].type && token.value === tokensB[index].value);
}
return {
BinaryExpression(node) {
const operators = new Set(["===", "==", "!==", "!=", ">", "<", ">=", "<="]);
if (operators.has(node.operator) && hasSameTokens(node.left, node.right)) {
context.report({ node, messageId: "comparingToSelf" });
}
}
};
}
};