prefer-for-of.js
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"use strict";
var __createBinding = (this && this.__createBinding) || (Object.create ? (function(o, m, k, k2) {
if (k2 === undefined) k2 = k;
Object.defineProperty(o, k2, { enumerable: true, get: function() { return m[k]; } });
}) : (function(o, m, k, k2) {
if (k2 === undefined) k2 = k;
o[k2] = m[k];
}));
var __setModuleDefault = (this && this.__setModuleDefault) || (Object.create ? (function(o, v) {
Object.defineProperty(o, "default", { enumerable: true, value: v });
}) : function(o, v) {
o["default"] = v;
});
var __importStar = (this && this.__importStar) || function (mod) {
if (mod && mod.__esModule) return mod;
var result = {};
if (mod != null) for (var k in mod) if (k !== "default" && Object.prototype.hasOwnProperty.call(mod, k)) __createBinding(result, mod, k);
__setModuleDefault(result, mod);
return result;
};
Object.defineProperty(exports, "__esModule", { value: true });
const experimental_utils_1 = require("@typescript-eslint/experimental-utils");
const util = __importStar(require("../util"));
exports.default = util.createRule({
name: 'prefer-for-of',
meta: {
type: 'suggestion',
docs: {
description: 'Prefer a ‘for-of’ loop over a standard ‘for’ loop if the index is only used to access the array being iterated',
category: 'Stylistic Issues',
recommended: false,
},
messages: {
preferForOf: 'Expected a `for-of` loop instead of a `for` loop with this simple iteration.',
},
schema: [],
},
defaultOptions: [],
create(context) {
function isSingleVariableDeclaration(node) {
return (node !== null &&
node.type === experimental_utils_1.AST_NODE_TYPES.VariableDeclaration &&
node.kind !== 'const' &&
node.declarations.length === 1);
}
function isLiteral(node, value) {
return node.type === experimental_utils_1.AST_NODE_TYPES.Literal && node.value === value;
}
function isZeroInitialized(node) {
return node.init !== null && isLiteral(node.init, 0);
}
function isMatchingIdentifier(node, name) {
return node.type === experimental_utils_1.AST_NODE_TYPES.Identifier && node.name === name;
}
function isLessThanLengthExpression(node, name) {
if (node !== null &&
node.type === experimental_utils_1.AST_NODE_TYPES.BinaryExpression &&
node.operator === '<' &&
isMatchingIdentifier(node.left, name) &&
node.right.type === experimental_utils_1.AST_NODE_TYPES.MemberExpression &&
isMatchingIdentifier(node.right.property, 'length')) {
return node.right.object;
}
return null;
}
function isIncrement(node, name) {
if (!node) {
return false;
}
switch (node.type) {
case experimental_utils_1.AST_NODE_TYPES.UpdateExpression:
// x++ or ++x
return (node.operator === '++' && isMatchingIdentifier(node.argument, name));
case experimental_utils_1.AST_NODE_TYPES.AssignmentExpression:
if (isMatchingIdentifier(node.left, name)) {
if (node.operator === '+=') {
// x += 1
return isLiteral(node.right, 1);
}
else if (node.operator === '=') {
// x = x + 1 or x = 1 + x
const expr = node.right;
return (expr.type === experimental_utils_1.AST_NODE_TYPES.BinaryExpression &&
expr.operator === '+' &&
((isMatchingIdentifier(expr.left, name) &&
isLiteral(expr.right, 1)) ||
(isLiteral(expr.left, 1) &&
isMatchingIdentifier(expr.right, name))));
}
}
}
return false;
}
function contains(outer, inner) {
return (outer.range[0] <= inner.range[0] && outer.range[1] >= inner.range[1]);
}
function isAssignee(node) {
var _a;
const parent = node.parent;
if (!parent) {
return false;
}
// a[i] = 1, a[i] += 1, etc.
if (parent.type === experimental_utils_1.AST_NODE_TYPES.AssignmentExpression &&
parent.left === node) {
return true;
}
// delete a[i]
if (parent.type === experimental_utils_1.AST_NODE_TYPES.UnaryExpression &&
parent.operator === 'delete' &&
parent.argument === node) {
return true;
}
// a[i]++, --a[i], etc.
if (parent.type === experimental_utils_1.AST_NODE_TYPES.UpdateExpression &&
parent.argument === node) {
return true;
}
// [a[i]] = [0]
if (parent.type === experimental_utils_1.AST_NODE_TYPES.ArrayPattern) {
return true;
}
// [...a[i]] = [0]
if (parent.type === experimental_utils_1.AST_NODE_TYPES.RestElement) {
return true;
}
// ({ foo: a[i] }) = { foo: 0 }
if (parent.type === experimental_utils_1.AST_NODE_TYPES.Property &&
parent.value === node &&
((_a = parent.parent) === null || _a === void 0 ? void 0 : _a.type) === experimental_utils_1.AST_NODE_TYPES.ObjectExpression &&
isAssignee(parent.parent)) {
return true;
}
return false;
}
function isIndexOnlyUsedWithArray(body, indexVar, arrayExpression) {
const sourceCode = context.getSourceCode();
const arrayText = sourceCode.getText(arrayExpression);
return indexVar.references.every(reference => {
const id = reference.identifier;
const node = id.parent;
return (!contains(body, id) ||
(node !== undefined &&
node.type === experimental_utils_1.AST_NODE_TYPES.MemberExpression &&
node.property === id &&
sourceCode.getText(node.object) === arrayText &&
!isAssignee(node)));
});
}
return {
'ForStatement:exit'(node) {
if (!isSingleVariableDeclaration(node.init)) {
return;
}
const declarator = node.init.declarations[0];
if (!declarator ||
!isZeroInitialized(declarator) ||
declarator.id.type !== experimental_utils_1.AST_NODE_TYPES.Identifier) {
return;
}
const indexName = declarator.id.name;
const arrayExpression = isLessThanLengthExpression(node.test, indexName);
if (!arrayExpression) {
return;
}
const [indexVar] = context.getDeclaredVariables(node.init);
if (isIncrement(node.update, indexName) &&
isIndexOnlyUsedWithArray(node.body, indexVar, arrayExpression)) {
context.report({
node,
messageId: 'preferForOf',
});
}
},
};
},
});
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