JavaScript Functions

Javascript Function

A Javascript function is a group of statements that performs specific tasks. It is mainly used due to avoid code repetition and It is reused again and again as per requirement.

Function Declarations

Javascript function can be declared using function keyword followed by the function name, then parentheses (), and then code written inside curly brackets {}.

General Syntax

function function_name(){
  //function statement
}

Function Expression

General Syntax

var addNumber=function(){
   // code inside
};

Calling a function

Javascript function can be called by function name followed by parenthesis, i.e ().

If a function name is addNumber, then use addNumber() to call the function.

General Syntax

functionName(); //calling function
function functionName() {}
functionName(); //calling  function

Anonymous Expression

There is another way to create a function using function expression. In this, a variable is declared and then assigned an anonymous to that variable. Since this function does not have a name so it is also known as an anonymous function.

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A javascript function expression is only invoked after the function. If function expression is called before the function then it generates an error.

General Syntax

jsFunction();
var jsFunction = function () {};
jsFunction();

Function Return Value

Javascript each function returns a value. Function default return value is undefined for all functions that do not contain a return statement. The function return value might be a string, number, function, array, or object.

Function returns undefined

function sayHello() {
  var x = "Hello ,i am learning javascript.";
}
sayHello(); // return undefined

Function returns string

function sayHello() {
  return "I am learning js .";
}
sayHello(); // return "hello"

Function Returns Number

General Syntax

function functionName(a, b) {
  return a + b;
}
functionName(x, y);

Function returns function

The function can also return a function. Both Functions return a function and callback.

General Syntax

function functionName() {
  return function () {
    return "something";
  };
}
functionName();
functionName()();

To read more about Javascript function, click here.