Count Items Matching a Rule

45.5% Acceptance

In this lab, you will be implementing a function called countMatches that takes two inputs: an array items, where each items[i] = [typei, colori, namei] describes the type, color, and name of the ith item, and a rule represented by two strings, ruleKey and ruleValue.

The function should return the number of items that match the given rule. An item is said to match the rule if one of the following is true:

  • ruleKey == "type" and ruleValue == typei.
  • ruleKey == "color" and ruleValue == colori.
  • ruleKey == "name" and ruleValue == namei.

Example 1:

countMatches([["phone","blue","pixel"],["computer","silver","lenovo"],["phone","gold","iphone"]], "color", "silver")

Output: 1

Explanation: There is only one item matching the given rule, which is ["computer","silver","lenovo"].

Example 2:

countMatches([["phone","blue","pixel"],["computer","silver","phone"],["phone","gold","iphone"]], "type", "phone")

Output: 2

Explanation: There are only two items matching the given rule, which are ["phone","blue","pixel"] and ["phone","gold","iphone"]. Note that the item ["computer","silver","phone"] does not match.


  • 1 <= items.length <= 104
  • 1 <= typei.length, colori.length, namei.length, ruleValue.length <= 10
  • ruleKey is equal to either "type", "color", or "name".
  • All strings consist only of lowercase letters.


  1. Write a function countMatches that takes array items, string ruleKey, string ruleValue, and returns the number of items that match the given rule. Export the function using ESM.

  2. Ensure that your function has proper error handling and check for edge cases.

Evaluation Script

You'll test your solution using the following evaluation script, in which two challenges are tested. To pass the lab, make sure your code is well-formatted, error-free, and follows the constraints and guidelines mentioned above.

import fs from 'fs' import { countMatches } from '/home/damner/code/index.js' // testlog is a log of test results const testlog = [] // this first block matches with - Challenge 1 try { const result = countMatches([["phone","blue","pixel"],["computer","silver","lenovo"],["phone","gold","iphone"]], "color", "silver") // perform some testing if(result === 1) { testlog.push({ status: 'pass' }) } else { throw new Error('Function countMatches is not working correctly') } } catch(error) { testlog.push({ status: 'error', error: error.message || 'Challenge 1 failed' }) } // this second block matches with - Challenge 2 try { const result2 = countMatches([["phone","blue","pixel"],["computer","silver","phone"],["phone","gold","iphone"]], "type", "phone") // perform some testing if(result2 === 2) { testlog.push({ status: 'pass' }) } else { throw new Error('Function countMatches is not handling edge cases correctly') } } catch(error) { testlog.push({ status: 'error', error: error.message || 'Challenge 2 failed' }) } // very important for the final length of `testlog` array to match the number of challenges, in this case - 2. // write the test log fs.writeFileSync('/home/damner/code/.labtests/testlog.json', JSON.stringify(testlog)) // write the results array boolean. this will map to passed or failed challenges depending on the boolean value at the challenge index fs.writeFileSync(process.env.UNIT_TEST_OUTPUT_FILE, JSON.stringify( => result.status === 'pass')))

Remember to export the countMatches function in your code using ESM. Follow the guidelines and constraints in the lab description, and ensure that your code works perfectly with the evaluation script above.

Setting up Test Environment Script

#!/bin/bash set -e 1 mkdir -p /home/damner/code/.labtests cat > /home/damner/code/.labtests/package.json << EOF { "type": "module" } EOF cd /home/damner/code/.labtests mv $TEST_FILE_NAME ./nodecheck.test.js # import puppeteer doesn't work without it npm link puppeteer node nodecheck.test.js 2>&1 | tee evaluationscript.log

Initial File System for User

// index.js /** * @param {string[][]} items * @param {string} ruleKey * @param {string} ruleValue * @return {number} */ export const countMatches = function(items, ruleKey, ruleValue) { };
// package.json { "name": "codedamn-lab", "type": "module" }
tabs: ['index.js'] terminals: ['yarn install']