1.

What are callbacks?

Answer»

A callback is a function that will be executed after another function gets executed. In javascript, functions are treated as first-class citizens, they can be used as an argument of another function, can be returned by another function, and can be used as a property of an object.

Functions that are used as an argument to another function are called callback functions. Example:

function divideByHalf(sum){
console.log(Math.floor(sum / 2));
}

function multiplyBy2(sum){
console.log(sum * 2);
}

function operationOnSum(num1,num2,operation){
var sum = num1 + num2;
operation(sum);
}

operationOnSum(3, 3, divideByHalf); // Outputs 3

operationOnSum(5, 5, multiplyBy2); // Outputs 20

  • In the code above, we are performing mathematical operations on the sum of two numbers. The operationOnSum function takes 3 arguments, the first number, the second number, and the operation that is to be performed on their sum (callback).

  • Both divideByHalf and multiplyBy2 functions are used as callback functions in the code above.

  • These callback functions will be executed only after the function operationOnSum is executed.

  • Therefore, a callback is a function that will be executed after another function gets executed.


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