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/**
* @fileoverview enforce "for" loop update clause moving the counter in the right direction.(for-direction)
* @author Aladdin-ADD<hh_2013@foxmail.com>
*/
"use strict";
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
module.exports = {
meta: {
docs: {
description: "enforce \"for\" loop update clause moving the counter in the right direction.",
category: "Possible Errors",
recommended: false,
url: "https://eslint.org/docs/rules/for-direction"
},
fixable: null,
schema: []
},
create(context) {
/**
* report an error.
* @param {ASTNode} node the node to report.
* @returns {void}
*/
function report(node) {
context.report({
node,
message: "The update clause in this loop moves the variable in the wrong direction."
});
}
/**
* check UpdateExpression add/sub the counter
* @param {ASTNode} update UpdateExpression to check
* @param {string} counter variable name to check
* @returns {int} if add return 1, if sub return -1, if nochange, return 0
*/
function getUpdateDirection(update, counter) {
if (update.argument.type === "Identifier" && update.argument.name === counter) {
if (update.operator === "++") {
return 1;
}
if (update.operator === "--") {
return -1;
}
}
return 0;
}
/**
* check AssignmentExpression add/sub the counter
* @param {ASTNode} update AssignmentExpression to check
* @param {string} counter variable name to check
* @returns {int} if add return 1, if sub return -1, if nochange, return 0
*/
function getAssignmentDirection(update, counter) {
if (update.left.name === counter) {
if (update.operator === "+=") {
return 1;
}
if (update.operator === "-=") {
return -1;
}
}
return 0;
}
return {
ForStatement(node) {
if (node.test && node.test.type === "BinaryExpression" && node.test.left.type === "Identifier" && node.update) {
const counter = node.test.left.name;
const operator = node.test.operator;
const update = node.update;
if (operator === "<" || operator === "<=") {
// report error if update sub the counter (--, -=)
if (update.type === "UpdateExpression" && getUpdateDirection(update, counter) < 0) {
report(node);
}
if (update.type === "AssignmentExpression" && getAssignmentDirection(update, counter) < 0) {
report(node);
}
} else if (operator === ">" || operator === ">=") {
// report error if update add the counter (++, +=)
if (update.type === "UpdateExpression" && getUpdateDirection(update, counter) > 0) {
report(node);
}
if (update.type === "AssignmentExpression" && getAssignmentDirection(update, counter) > 0) {
report(node);
}
}
}
}
};
}
};
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