Functions that take or return other functions
In JavaScript programming, user-created functions are passed as arguments to other functions between actual and formal arguments, and other user-created program functions can also be returned. Function returns are a powerful feature of JavaScript programming. Where function features help JavaScript programmers to use higher-order, function closure features and features like callback functions and functional programming.
So, let’s understand the process of passing arguments to a function in JavaScript programming.
JavaScript functions that deal with other functions as arguments.
User-defined functions in JavaScript programs deal with other program functions as arguments. This feature is mostly found in callback functions, where a user-declared function is executed after another function completes its process.
Passing function as argument in JavaScript callback example.
function message(compname, callback) {
console.log(`Vcanhelpsu, ${compname}`);
callback();
}
function youcanjoin() {
console.log(“Get your free digital resources”);
}
message(“Harry”, youcanjoin);
Passing function as argument in JavaScript callback explained.
In this example, the message function inputs a name and a callback function as input arguments. It calls the callback() function after displaying the company name. And passes the Get your free digital resources message as the callback function.
Why use function as argument in JavaScript program.
- Asynchronous programming – Asynchronous is a basic concept in JavaScript programming, where a function can be passed as a callback function in a program to execute asynchronous tasks in the current program after they have completed.
- Custom behavior – Passing a user-created custom function as an argument in a JavaScript program and providing permission allows the calling function to customize its behavior.
Functions in JavaScript programs that return other functions.
A function in JavaScript program can also return another function value. Function factories, closures, and secure and private functions help programmers to create such functions.
Example of a function returning another function value.
function product(fact) {
return function(integer) {
return integer * fact;
};
}
const single = product(1); // here single is now a function that single integer value
console.log(single(7)); // Result – 7
const double = product(2); // here double now a function that double integer value
console.log(double(10)); // Output: 15
Explanation of function returning another function value.
In this program, the product function inputs a product value, and returns a new function value that multiplies the argument to the function by that product. Where the returned function “holds” the product, due to the closure function features, we can create multiple functions like single and double, which behave differently.
Why function values are returned in JavaScript programs.
- Currying – This feature helps JavaScript programmers to create specific versions of functions by partially applying arguments.
- Function Factory – JavaScript programmers can create customized functions for multiple tasks without repeating the function program code.
Example of higher-order function in JavaScript.
A higher-order function in JavaScript program function is one that takes either one or more functions in a program as input value arguments, where it returns a function value to the current program, or both function values.
Higher-order function examples in JavaScript.
function selectcourse(programming) {
return function(programmingname) {
if (programming === “prog1”) {
return “Javascript, ” + programmingname;
} else if (programming === “prog2”) {
return “Python, ” + programmingname;
} else if (programming === “prog3”) {
return “Html, ” + programmingname;
}
};
}
const selectjavascript = selectcourse(“prog1”);
const selectpython = selectcourse(“prog2”);
const selecthtml = selectcourse(“prog3”);
console.log(selectjavascript(“Harry”)); // Result – Javascript, Harry
console.log(selectpython(“Bhavishi”)); // Result – Python, Bhavishi
console.log(selecthtml(“Siddhi”)); // Result – Html, Siddhi
Explanation of Higher-order function.
In this program, the selectcourse() function returns a new function value based on the programming argument. The returned function can be used to provide a selection of people in various programming language courses. Where, selectcourse() is a user-created higher-order function. Because it returns a function value.
Practical Uses of JavaScript Functions.
Event handlers using functions as arguments in a JavaScript program
A common realtime example of a function that inputs or returns values to other functions in a program is when working with event handler features in a JavaScript program. For example, event handler features can be applied when using setTimeout or DOM events.
Example of an event handler using a callback function in a JavaScript program.
function pressbutton(callback) {
console.log(“Button pressed”);
callback();
}
function displayinfo() {
console.log(“You press the button”);
}
pressbutton(displayinfo);
Explanation of event handler using a callback function.
In this program example, pressbutton inputs a function (displayinfo) as an argument, and calls it in a callback function after logging the message “Button pressed!” to simulate handling event handler conditions such as a button press.
Example of a function returning a function to handle customization in JavaScript.
So, let’s understand the use of function returns and closures to create a customizable logging function in a JavaScript program.
Example of a JavaScript customizable logging function.
function logfile(prefix) {
return function(info) {
console.log(`${prefix} – ${info}`);
};
}
const infoLogfile = logfile(“INFORMATION”);
const warnLogfile = logfile(“WARNING”);
const deleteLogfile = logfile(“DELETE”);
infoLogfile(“This is a info logfile information”); // Result – INFORMATION – This is a info logfile information
warnLogfile(“This is a info warnlogfile information”); // Result – WARNING – This is a info warnfile information
deleteLogfile(“This is a info deletelogfile information”); // Result – DELETE – This is a info deletelogfile information
Explanation of JavaScript customizable logging function.
Here logfile returns a new logging function value customized with the given prefix. Where each returned logfile function holds its specific prefix value, and uses it to log log file messages.
Example of function returning function with closure in JavaScript program.
Closure concept in JavaScript program allows internal function to hold and access function variables declared from its external function.
Example of function returning function with access to external variables.
function developtester() {
let tester = 1; // here declare tester as a private variable
return {
increment: function() {
tester++;
console.log(tester);
},
decrement: function() {
tester–;
console.log(tester);
},
gettester: function() {
return tester;
}
};
}
const tester = developtester();
Explanation of function returning function with access to external variables.
Here developtester() returns an object value that contains program functions that can manipulate and access the tester variable. While the tester variable is not externally accessible in the object, functions inside the function object can access it through closures.
Conclusion of Functions that take or return other functions in JavaScript.
- JavaScript programs are user-declared functions that take other functions as arguments. These features allow JavaScript programmers to implement callbacks and asynchronous programming operations in their programs.
- Functions that return other functions: Functions in a JavaScript program that return either another function value or a function argument can create customized behavior or function factories in an existing program, and are mostly implemented in closures.
- Higher-order functions Functions in a JavaScript program are user-generated functions that take either another function as arguments or return a function value or both if they meet certain conditions.
