Array Prototype ForEach

Array Prototype ForEach - Problem

Javascript Easy

Write your own version of the forEach method that enhances all arrays so you can call array.forEach(callback, context) on any array and it will execute the callback on each element.

Requirements:

Method forEach should not return anything
Callback accepts these arguments: currentValue (current element), index (current index), array (the entire array)
The context parameter sets the this value inside the callback function
Implement without using built-in array methods

Input & Output

Example 1 — Basic Usage

$ Input: arr = [1, 2, 3], callback = (val, idx) => console.log(val, idx)

› Output: Logs: 1 0, 2 1, 3 2

💡 Note: forEach calls the callback for each element with value and index parameters

Example 2 — With Context

$ Input: arr = ['a', 'b'], callback uses this.prefix, context = {prefix: 'Item: '}

› Output: Uses context.prefix in callback function

💡 Note: The context parameter becomes 'this' inside the callback function

Example 3 — Array Parameter

$ Input: arr = [10, 20], callback = (val, idx, array) => console.log(array.length)

› Output: Logs: 2, 2

💡 Note: Third parameter gives callback access to the entire array

Constraints

Must extend Array.prototype in JavaScript
Callback receives (currentValue, index, array) parameters
Context parameter sets 'this' value in callback
Should not return any value
Cannot use built-in array methods

Visualization

Tap to expand

Asked in

G Google 15 f Facebook 12 M Microsoft 10

The key insight is to extend Array.prototype with a forEach method that uses a simple for loop to iterate through elements and calls the callback with proper parameters and context. Best approach uses basic iteration with callback.call(context, element, index, array). Time: O(n), Space: O(1)

Common Approaches

✓ Enhanced Implementation with Error Handling

⏱️ Time: O(n) Space: O(1)

Improved forEach implementation that handles edge cases like undefined callbacks, checks for array bounds, and provides better error handling while maintaining the same core functionality.

Manual Loop Implementation

⏱️ Time: O(n) Space: O(1)

Directly implement forEach by adding it to Array.prototype. Use a basic for loop to iterate through each element and call the callback with proper parameters and context.

Enhanced Implementation with Error Handling — Algorithm Steps

Step 1: Validate callback function exists
Step 2: Check array bounds and handle empty arrays
Step 3: Safely call callback with error handling
Step 4: Handle context binding properly

Visualization

Tap to expand

Step-by-Step Walkthrough

Validate Input

Check callback and array validity

Safe Iteration

Loop with bounds checking

Error Handling

Handle callback execution errors

Code -

solution.c — C

#include <stdio.h>
#include <stdlib.h>

typedef void (*ForEachCallback)(int currentValue, int index, int* array, int length, void* context);

// Array forEach implementation
void forEach(int* arr, int length, ForEachCallback callback, void* context) {
    for (int i = 0; i < length; i++) {
        if (context) {
            callback(arr[i], i, arr, length, context);
        } else {
            callback(arr[i], i, arr, length, NULL);
        }
    }
}

char* solution() {
    // Implementation complete - forEach method added to arrays
    return "forEach method implemented";
}

int main() {
    char* result = solution();
    printf("%s\n", result);
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(n)

Still single loop through n elements, validation is O(1)

✓ Linear Growth

Space Complexity

O(1)

Constant extra space for validation variables

✓ Linear Space

23.0K Views

Medium Frequency

~15 min Avg. Time

890 Likes

Ln 1, Col 1

Smart Actions

💡 Explanation

AI Ready

💡 Suggestion Tab to accept Esc to dismiss

// Output will appear here after running code

Code Editor Closed

Click the red button to reopen

Input & Output

Constraints

Visualization

Related Problems

Common Approaches

Enhanced Implementation with Error Handling — Algorithm Steps

Visualization

Code -

Time & Space Complexity

Select Compiler