Introduction to Functions

Functions cannot be overloaded in JS: Function defined with n arguments can be passed with n args where extra args will be ignored.

function foo() {
return "Hello World";
}
foo();

Functions can be created as

  1. Function Expression
  2. Anonymous Function Expression
  3. Functions as arguments
  4. Functions on objects

1. Function Expression
Functions as values (FIRST CLASS CITIZENS)
var myFunc = function foo() {
return "Hello World";
}
myFunc();

2. Anonymous Function Expression
In the below expression function name is not required as we call with assigned variable anyways which is aka AFE
var myFunc = function() {
return "Hello World";
}
myFunc();

3. Functions as Arguments
var myFunc = function() {
return "Hello World";
}
var executorFunc = function(fn) {
fn();
}
executorFunc(myFunc);

4. Functions on Objects
var myObj = {
"prop1": true
}
myObj.myFunc = function() {
console.log("Hello World");
}
console.log(myObj);
myObj.myFunc();

Default Function Arguments
‘arguments’: is an indexed object with list of arguments passed to method
‘this’: Understanding ‘this’ keyword in JS
var person = {
"firstName": "Niranjan",
"lastName": "Tallapalli",
"getFullName": function() {
console.log(person.firstName + ' ' + person.lastName);
}
}

person.getFullName(); // would work fine BUT
// imagine this scenario
var person2 = person; // object address is copied
person = {};
person2.getFullName(); // this would have person reference which is empty hence results in “undefined undefined”
// instead refer to the object on which getFullName is invoked which is done via “this” keyword

Note: *** Functions are objects behind the scenes in JS ***

Array functions
myArr.push(element); // will add element at the end of an array
myArr.pop(); // will remove last element from array
myArr.shift(); // removes element from beginning of array
myArr.unshift(element); // push element at the beginning of array
myArr.forEach(function(item, index, arr) {
console.log(item +' '+index);
})

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