Javascript | Notes 2

Understanding Callbacks

• Call backs are just functions passed into other functions as arguments.

• Below is the code for understanding callbacks. The below code may show you how forEach might look under the hood.

const customForLoop = (arr, callback) => {
    for (let i = 0; i < arr.length; i++) {
        callback(arr[i]);
    }
}

const inputArray = [1,2,3,4];

customForLoop(inputArray, (item) => {
    console.log(item * 2);
})

• Here, in the above code item is passed into the callback function

Event Listeners

• Below is a simple code for an event listener

const element = document.querySelector("#elementId");
button.addEventListener('click', (event) => {
    console.log(event.target.value)
})

• Here, in the above code, the second value that is being passed is a function