You can create JavaScript nested functions by writing one function inside another function. Make a call to the inner function in the return statement of the outer function.
function A(){
B(); //call should be B();
function B(){
//code
}
}Here’s an example of how to create and use nested functions:
function outerFunction() {
const outerVariable = "I'm from the outer function";
function innerFunction() {
const innerVariable = "I'm from the inner function";
console.log(outerVariable); // Accessing the outer variable
console.log(innerVariable); // Accessing the inner variable
}
innerFunction(); // Call the inner function
}
outerFunction(); // Call the outer function
In this example, we have an outerFunction containing an innerFunction. The innerFunction can access variables from the outerFunction, such as outerVariable, because it’s nested inside the outerFunction. When you call outerFunction, it also calls innerFunction from within it.
JavaScript nested function
Simple example code.
<!DOCTYPE html>
<html>
<body>
<script>
function fun1(a) {
function fun2(b) {
return a + b;
}
return fun2;
}
function final() {
console.log(fun1('Outer')(' + Nested Function'))
}
final();
</script>
</body>
</html> Output:
Different ways to create and use nested function
<script>
function fun1(a) {
fun = function fun2(b) {
return a + b;
}
return fun;
}
function final() {
console.log(fun1('Hello')(' Function'))
}
final();
</script>Output: Hello Function
Write output on the HMTL page
<script>
function hypotenuse(a, b) {
function square(x) { return x*x; }
return Math.sqrt(square(a) + square(b));
}
function secondFunction() {
var result;
result = hypotenuse(1,2);
document.write (result);
}
secondFunction();
</script>Output: 2.23606797749979
Can you write nested functions in JavaScript?
Answer: Yes, it is possible to write and call a function nested in another function. You can also use it for calculation inside but define it outside.
There is a restriction that function definitions may not appear within loops or conditionals.
function a(x) { // <-- function
function b(y) { // <-- inner function
return x + y; // <-- use variables from outer scope
}
return b; // <-- you can even return a function.
}
console.log(a(3)(4));What’s the need and use of nested functions in JavaScript?
Answer: The core importance of nested functions is scope generation and achieving the following.
- Non-Polluted Global Namespace
- Modularization of functionality
- Encapsulate private internal workings of modules
- Prevent collision of identifiers across different scripts
- Smaller script sizes because variables inside nested scopes qualify for minification.
- It speeds up the Identifier Resolution Process
Source: stackoverflow.com
Do comment if you have any doubts or suggestions on this Js function topic.
Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.
OS: Windows 10
Code: HTML 5 Version