2 * @fileoverview Rule to flag use of unary increment and decrement operators.
3 * @author Ian Christian Myers
4 * @author Brody McKee (github.com/mrmckeb)
9 //------------------------------------------------------------------------------
11 //------------------------------------------------------------------------------
14 * Determines whether the given node is the update node of a `ForStatement`.
15 * @param {ASTNode} node The node to check.
16 * @returns {boolean} `true` if the node is `ForStatement` update.
18 function isForStatementUpdate(node) {
19 const parent = node.parent;
21 return parent.type === "ForStatement" && parent.update === node;
25 * Determines whether the given node is considered to be a for loop "afterthought" by the logic of this rule.
26 * In particular, it returns `true` if the given node is either:
27 * - The update node of a `ForStatement`: for (;; i++) {}
28 * - An operand of a sequence expression that is the update node: for (;; foo(), i++) {}
29 * - An operand of a sequence expression that is child of another sequence expression, etc.,
30 * up to the sequence expression that is the update node: for (;; foo(), (bar(), (baz(), i++))) {}
31 * @param {ASTNode} node The node to check.
32 * @returns {boolean} `true` if the node is a for loop afterthought.
34 function isForLoopAfterthought(node) {
35 const parent = node.parent;
37 if (parent.type === "SequenceExpression") {
38 return isForLoopAfterthought(parent);
41 return isForStatementUpdate(node);
44 //------------------------------------------------------------------------------
46 //------------------------------------------------------------------------------
53 description: "disallow the unary operators `++` and `--`",
54 category: "Stylistic Issues",
56 url: "https://eslint.org/docs/rules/no-plusplus"
63 allowForLoopAfterthoughts: {
68 additionalProperties: false
73 unexpectedUnaryOp: "Unary operator '{{operator}}' used."
79 const config = context.options[0];
80 let allowForLoopAfterthoughts = false;
82 if (typeof config === "object") {
83 allowForLoopAfterthoughts = config.allowForLoopAfterthoughts === true;
88 UpdateExpression(node) {
89 if (allowForLoopAfterthoughts && isForLoopAfterthought(node)) {
95 messageId: "unexpectedUnaryOp",
97 operator: node.operator