ForEach.md

forEach() method

The forEach() method in JavaScript is used to execute a provided function once for each array element. It does not return a new array like the map() method.

Here's how it works:

1. It is a method available on all arrays.
2. It executes a provided function once for each array element.
3. The provided function is called with three arguments: the current element, the index of the current element, and the array forEach() was called upon.
4. It does not mutate the original array.

Here's a simple example:

const numbers = [1, 2, 3, 4, 5];

numbers.forEach(function(number, index) {
    console.log(`Element ${number} is at index ${index}`);
});

// Output:
// Element 1 is at index 0
// Element 2 is at index 1
// Element 3 is at index 2
// Element 4 is at index 3
// Element 5 is at index 4

In this example, forEach() is called on the numbers array and logs each number along with its index.

Syntax

The syntax for the forEach() method in JavaScript is as follows:

array.forEach(callbackFunc(currentValue, index, arr), thisValue)

Here's what each parameter means:

• callbackFunc(currentValue, index, arr): A function to be called for each element in the array. This function accepts three arguments:
  • currentValue: The current element being processed in the array.
  • index (optional): The index of the current element being processed in the array.
  • arr (optional): The array forEach was called upon.
• thisValue (optional): A value to use as this when executing the callback function.

Polyfill

const numbers = [1, 2, 3, 4, 5];

Array.prototype.forEach = function(callbackFunc){
    for(let i=0; i<this.length; i++){
        callbackFunc(this[i])
    }
}

const printNums = function(number, index) {
    console.log(`Element ${number} is at index ${index}`);
}

numbers.forEach(printNums) 

// Output:
// Element 1 is at index 0
// Element 2 is at index 1
// Element 3 is at index 2
// Element 4 is at index 3
// Element 5 is at index 4