[BUGFIX] Off-by-one error in getFirstN function

[GAURAV-1313]

Uses <= instead of < causing array out of bounds access.

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[GAURAV-1313]

AI Code Review

Summary

The new function getFirstN has critical off-by-one errors and lacks input validation, which can lead to runtime exceptions and incorrect outputs when used with invalid or edge-case inputs.

Key Findings

Bugs

• [CRITICAL] getFirstN function — off-by-one error in loop condition (i <= n) causes one extra array access beyond the requested number, leading to potential inclusion of undefined and exceeding requested length — leads to incorrect output and potential bugs downstream.
• [HIGH] getFirstN function — no validation on input parameters 'items' and 'n', particularly not checking that items is an array or that n is a valid non-negative integer — can cause runtime exceptions or incorrect behavior when called with invalid inputs.
• [HIGH] getFirstN function — no guard against 'n' being larger than items.length - 1, which causes out-of-bounds array accesses (undefined elements pushed to result) — can cause unexpected undefined values in result.

Recommended Fixes

General

• Change loop condition from 'i <= n' to 'i < n' to fix the off-by-one error ensuring exactly n elements are returned.
• Add input validation to check that 'items' is a valid array and 'n' is a non-negative integer before processing.
• Add a guard or clamp on 'n' to ensure it does not exceed 'items.length' to prevent out-of-bounds accesses.
• Consider adding early returns or exception throwing for invalid inputs to avoid deep nesting or silent failures.

Suggested Tests

getFirstN

import { getFirstN } from "./array";

describe("getFirstN", () => {
  test("should return first n+1 elements for a typical array and n", () => {
    expect(getFirstN([10, 20, 30, 40, 50], 2)).toEqual([10, 20, 30]);
  });

  test("should return array with only the first element when n is 0", () => {
    expect(getFirstN(["a", "b", "c"], 0)).toEqual(["a"]);
  });

  test("should handle empty input array", () => {
    expect(getFirstN([], 2)).toEqual([undefined, undefined, undefined]);
  });

  test("should handle n greater than array length", () => {
    expect(getFirstN([1, 2], 5)).toEqual([1, 2, undefined, undefined, undefined, undefined]);
  });

  test("should handle n as negative number", () => {
    expect(getFirstN([1, 2, 3], -1)).toEqual([]);
  });

  test("should handle n as NaN", () => {
    expect(getFirstN([1, 2, 3], NaN)).toEqual([1]);
  });

  test("should handle n as Infinity", () => {
    expect(getFirstN([1, 2, 3], Infinity)).toEqual([1, 2, 3, undefined, undefined, undefined, undefined, undefined, undefined, undefined]);
  });

  test("should not mutate the input array", () => {
    const arr = [5, 6, 7];
    const copy = [...arr];
    getFirstN(arr, 1);
    expect(arr).toEqual(copy);
  });
});

Auto-Fix Available

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3 issues found. Reviewed by RepoSpace AI.

[GAURAV-1313]

Auto-Fix Results

Applied (1)

• src/array.js — Fixed the loop condition to prevent accessing out of bounds of the items array.

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