Function As First Class Citizen:
In Javascript we can pass function as parameter or return function
as parameter that is why function are called first class citizen.
Higher Order Function:
Function which take another function as parameter or return function
as return value is called higher order function.
Consider following code snippet
Code:
function HowAreYou() {
console.log("How are you ?");
}
function WhatsUp() {
console.log("What's up buddy ?");
}
function greet(relation, HowAreYou, WhatsUp) {
if (relation === "friend") {
WhatsUp();
} else if (relation === "familiar") {
HowAreYou();
}
}
// prints 'What's up?'
greet('familiar', HowAreYou, WhatsUp);
Output:
How are you ?
Note:
Here function greet takes function as its parameter so it is higher
border functions.
Native Higher Order function:
map,reduce,sort & filter are functions related to array in javascript
These are a higher order functions as they take take other functions
as parameter.
map() Example:
Code:
let objArr = [
{ name: "sangram", city: "kankavali" },
{ name: "sagar", city: "kolhapur" },
{ name: "sachin", city: "ratnagiri" },
{ name: "sandesh", city: "pune" },
{ name: "swapnil", city: "numbai" },
];
let nameArr = objArr.map((elt) => {
return elt.name;
});
console.log(nameArr);
Output:
[ 'sangram', 'sagar', 'sachin', 'sandesh', 'swapnil' ]
Reduce Example:
Code:
let objArr = [
{ name: "sangram", city: "kankavali", mark: 57 },
{ name: "sagar", city: "kolhapur", mark: 67 },
{ name: "sachin", city: "ratnagiri", mark: 78 },
{ name: "sandesh", city: "pune", mark: 89 },
{ name: "swapnil", city: "numbai", mark: 94 },
];
let sum = objArr.reduce((sum, elt) => {
return (sum += elt.mark);
}, 0);
console.log(sum);
Output:
385
FILTER Example:
Code:
let objArr = [
{ name: "sangram", city: "kankavali", mark: 57 },
{ name: "sagar", city: "kolhapur", mark: 67 },
{ name: "sachin", city: "ratnagiri", mark: 78 },
{ name: "sandesh", city: "pune", mark: 89 },
{ name: "swapnil", city: "numbai", mark: 94 },
];
let sixtyorAbove = objArr.filter((elt) => {
return elt.mark > 60;
});
console.log(sixtyorAbove);
Output:
[
{ name: 'sagar', city: 'kolhapur', mark: 67 },
{ name: 'sachin', city: 'ratnagiri', mark: 78 },
{ name: 'sandesh', city: 'pune', mark: 89 },
{ name: 'swapnil', city: 'numbai', mark: 94 }
]
SORT Example:
Code:
let objArr = [
{ name: "sangram", city: "kankavali", mark: 57 },
{ name: "sagar", city: "kolhapur", mark: 67 },
{ name: "sachin", city: "ratnagiri", mark: 78 },
{ name: "sandesh", city: "pune", mark: 89 },
{ name: "swapnil", city: "numbai", mark: 94 },
];
let sortedArray = objArr.sort((a, b) => {
return a.mark > b.mark;
});
console.log(sortedArray);
Output:
[
{ name: 'sangram', city: 'kankavali', mark: 57 },
{ name: 'sagar', city: 'kolhapur', mark: 67 },
{ name: 'sachin', city: 'ratnagiri', mark: 78 },
{ name: 'sandesh', city: 'pune', mark: 89 },
{ name: 'swapnil', city: 'numbai', mark: 94 }
]
Function Returning another function:
Code:
function Apple(type) {
this.type = type;
this.color = "red";
this.getInfo = function () {
let msg = this.color + " " + this.type + " apple";
return function () {
console.log(msg);
};
};
}
let app = new Apple("himachal");
let getInfoFunc = app.getInfo();//getInfoFunc is a function
getInfoFunc()
Output:
red himachal apple
Explanation:
Here function getInfo return another anonymous function.
Note:
let app = new Apple("himachal");
This statement creates a new object instance of the Apple constructor
with the type property set to "himachal",color property ro "red"
and assigns it to the variable app.
On contratory
let app = Apple("himachal");
This statement calls the Apple constructor function but does not create a
new object instance because the new keyword is missing. As a result, app
will be undefined because the constructor function does not return anything
explicitly.
The new keyword is technically optional when calling a constructor function
in JavaScript. When you call a function using new, it creates a new object
and sets the function's prototype (i.e., this) to that object, which is the
typical behavior for a constructor function.
However, if you omit new when calling a constructor function, the function
still executes, but it behaves more like a regular function rather than a
constructor. It does not create a new object, and it does not implicitly
return this. Therefore, if your constructor function relies on this to set
properties or behaviors of the new object, omitting new will not work as
expected.
