JavaSript Callback Function Tutorial

https://www.youtube.com/watch?v=pTbSfCT42_M

Sample 1

This is a simple JavaSript callback function usage:

let x = function(){
    console.log('this is a')
}

let y = function(call){
    console.log('this is b');
    call();
}

y(x)

Output:

this is b
this is a

Sample 2

Before callback:

let calc = function(num1, num2, calcType) {
    if (calcType === "add") {
        return num1 + num2;
    } else if (calcType === "multiply") {
        return num1 * num2;
    }
};

console.log(calc(2, 3, 'add'));
console.log(calc(2, 3, 'multiply'));

After callback:

let add = function(a, b) {
    return a + b;
};

let multiply = function(a, b) {
    return a * b;
};

let calc = function(num1, num2, callback) {
    if (typeof callback === "function") {
        return callback(num1, num2);
    } else {
        return 'Error...';
    }
};

console.log(calc(2, 3, add));
console.log(calc(2, 3, 'add'));  // Error...
console.log(calc(2, 3, multiply));

console.log(calc(2, 3, function(a, b) {
    return a - b;
}));
console.log(calc(2, 3, (a, b) => {
    return a - b;
}));