Map.md

map() method

The map() method in JavaScript works as follows:

1. It creates a new array with the results of calling a provided function on every element in the calling array.
2. The provided function is called with three arguments: the current element, the index of the current element, and the array map was called upon.
3. The this value provided as a second argument to map() is used as this when executing each callback.
4. It does not mutate the original array.

Here's a simple example:

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

const doubledNumbers = numbers.map(function(number) {
    return number * 2;
});

console.log(doubledNumbers); // Output: [2, 4, 6, 8, 10]

In this example, map() is called on the numbers array and returns a new array doubledNumbers where each number is doubled.

Syntax

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

array.map(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 map 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.map = function(callbackFunc){
    const newArr = []
    for(let i=0; i<this.length; i++){
        newArr.push(callbackFunc(this[i]))
    }
    return newArr;
}

console.log(numbers.map(doubledNumbers)) // Output: [2, 4, 6, 8, 10]