What is Function in JavaScript?
In JavaScript, functions are defined with the 'function' keyword.
- There is an another way to define a function, called 'Arrow Function'.
Declaration a Function
Syntax
function firstFunction () {
// Code here ...
}
Example
function firstFunction () {
console.log('JavaScript function');
}
firstFunction();
// JavaScript function
Function Expressions
A function expression can be stored in a variable.
Syntax
let firstFunction = function () {
// Code here ...
}
Example
let firstFunction = function () {
return "JavaScript function";
}
firstFunction();
// JavaScript function
Arrow Function
Arrow function allows a short syntax for writing function expressions.
- We don't need the 'function' keyword, the 'return' keyword and the 'curly' brackets.
Syntax
let change = (argument1, argument2) => Code here ... ;
Example:
let add = (x , y) => x + y;
add(4, 6);
// Output will 10
Function Parameters
If you want to build a dynamic function then you have to use parameters.
- Parameters are like an input. Based on your input it gives you the output.
Syntax with example
function add(x, y) {
return (x + y);
}
add(10, 5); // Output: 15,
// Here, x is 10, y is 5.
Default Parameters
If a function is called with missing arguments, the missing values are set to undefined.
- It is better to assign a default value to the parameter.
Syntax
function myFunction (argument1 = default value) {
// Code here ...
}
Example
function sum (x = 1, y = 1) {
return (x + y);
}
sum(4, 6); // here x is 4, y is 6
sum(4); // here x is 4 but y is 1 (default value)
sum(); // here x is 1, y is 1
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