1/** 2 * @fileoverview Rule to flag the generator functions that does not have yield. 3 * @author Toru Nagashima 4 */ 5 6"use strict"; 7 8//------------------------------------------------------------------------------ 9// Rule Definition 10//------------------------------------------------------------------------------ 11 12module.exports = { 13 meta: { 14 type: "suggestion", 15 16 docs: { 17 description: "require generator functions to contain `yield`", 18 category: "ECMAScript 6", 19 recommended: true, 20 url: "https://eslint.org/docs/rules/require-yield" 21 }, 22 23 schema: [], 24 25 messages: { 26 missingYield: "This generator function does not have 'yield'." 27 } 28 }, 29 30 create(context) { 31 const stack = []; 32 33 /** 34 * If the node is a generator function, start counting `yield` keywords. 35 * @param {Node} node A function node to check. 36 * @returns {void} 37 */ 38 function beginChecking(node) { 39 if (node.generator) { 40 stack.push(0); 41 } 42 } 43 44 /** 45 * If the node is a generator function, end counting `yield` keywords, then 46 * reports result. 47 * @param {Node} node A function node to check. 48 * @returns {void} 49 */ 50 function endChecking(node) { 51 if (!node.generator) { 52 return; 53 } 54 55 const countYield = stack.pop(); 56 57 if (countYield === 0 && node.body.body.length > 0) { 58 context.report({ node, messageId: "missingYield" }); 59 } 60 } 61 62 return { 63 FunctionDeclaration: beginChecking, 64 "FunctionDeclaration:exit": endChecking, 65 FunctionExpression: beginChecking, 66 "FunctionExpression:exit": endChecking, 67 68 // Increases the count of `yield` keyword. 69 YieldExpression() { 70 71 /* istanbul ignore else */ 72 if (stack.length > 0) { 73 stack[stack.length - 1] += 1; 74 } 75 } 76 }; 77 } 78}; 79