Anonymous functions, function expressions, and callbacks
In JavaScript programming, functions are built-in programming concept, functions are declared in JavaScript program along with variables, passed as arguments to the declared program function, or even returned function value actual and formal arguments. Functions in JavaScript are highly helpful in modular programming flexible and functional programming method. Here in JavaScript, we will learn more about anonymous function, function expression and callback features.
Anonymous function JavaScript function.
An anonymous function in any JavaScript program is a function that does not have any declared variable name in the current program. Anonymous functions in JavaScript are mainly used when JavaScript programmer needs anonymous function in temporary order, and programmer does not need to reference anonymous function by name.
Syntax of anonymous function JavaScript function.
function(para1, para2, …) {
// Program code to be executed in the anonymous function
}
In JavaScript programs, anonymous functions are used in the expression or callback order given in the function.
Example of anonymous function JavaScript function.
JavaScript anonymous function.
let message = function(info) {
console.log(“Welcome to, ” + info + “|”);
};
message(“Vcanhelpsu”); // here it Calling an anonymous function in existing program
Explanation of anonymous function.
In the above program function, the value is assigned to the variable named message. Here the function has no name, but you can call it using the existing program variable message.
Function expression JavaScript function.
Function expression in JavaScript program is performed when a function is defined inside an expression in the JavaScript program. Where a function expression may be declared in the current program in either anonymous or named order. Variables in a function expression may be assigned values, passed as arguments to the function, or returned from another function.
The syntax of a function expression.
let functionName = function(para1, para2, …) {
// Program source code to be executed in the current program
};
Here a variable is assigned to the current function, or passed directly, and is not referenced in a function expression like a function declaration.
Example of an anonymous function expression.
let add = function(p, q) {
return p + q;
};
let output = add(9, 7);
console.log(output);
Example of a named function expression.
let divide = function divide(p, q) {
return p / q;
};
let output = divide(24, 4);
console.log(output);
Explanation of a function expression.
Here the function add is an anonymous function expression value in the current program, because here this function has no name.
Similarly the function divide is a named function expression value, here the name of this function is divide, which is necessary for debugging in a function program.
The main difference between function declarations and function expressions in JavaScript.
- Hoisting – Function declarations in JavaScript programs are of hoisted nature, due to this you can call the function in the program before defining it. Function expressions in the current program are not of hoisted nature, due to this they are called only after being assigned in the current program.
- Naming – Function expressions declared in JavaScript programs can be of anonymous or named nature. The same function declaration in the program is always named.
Callback JavaScript.
A callback function in a JavaScript program is a function that is passed as an argument to another function in the JavaScript program and is executed after the completion of a function task. Callback features are mostly used in JavaScript programs for asynchronous program operations, such as managing program events, processing data after a delay, or when the program is waiting for user input.
Example of callback JavaScript.
function message(info, callback) {
console.log(“Welcome to, ” + info + “,”);
callback(); // here callback function Calling the callback function
}
function text() {
console.log(“Get free programming material.”);
}
message(“Vcanhelpsu”, text);
Explanation of callback JavaScript.
Here the message function inputs two arguments, which are the name and the callback function.
After logging the message function, the message calls the callback function, which in this case is the text, “Welcome, vcanhelpsu” followed by “Get free programming material” message.
Example of callback with parameters.
function fetchData(url, callback) {
console.log(“Fetching website data ” + url);
let data = { message: “Url Data fetched successfully.” };
callback(data); // it use to Calling the callback with fetch data
}
function textMessage(data) {
console.log(data.message);
fetchData(“https://google.com”, textMessage);
Callback JavaScript Explained.
In this program, fetchData requests data from the given website URL, and then calls a callback in the current program, passing the received URL data as textMessage.
Callback set in asynchronous virtualization.
Callbacks are important in asynchronous virtualization in JavaScript programs. For example, scheduling a task with a timer, scheduling a task, or scheduling a user event.
Example of using callback with setTimeout in JavaScript.
function messagewithDelay(text, callback) {
setTimeout(function() {
console.log(“Welome to vcanhelpsu, ” + text + “|”);
callback(); // here callback funtion is Calling callback with delay
}, 4000); // it display message with a 4 seconds delay
}
function reply() {
console.log(“Thanks for wait”);
}
messagewithDelay(“Harry”, reply);
Remember.
In this program messageafterdelay uses setTimeout features to delay the message print.
Here after a delay of 4 seconds, it displays a text message in the screen, and then calls the reply callback.
Fantasy expression as JavaScript Arrow Satellite.
Arrow is a popular method of anonymous expression in JavaScript programs. Arrow anonymous function is used in JavaScript programs when you need immediate inline in a JavaScript program, in special condition callback can be used in condition order.
Syntax of Arrow in JavaScript.
functionName = (parameter1, parameter2) => {
//Program source code to be saved in the current program
};
Instance of Arrow Strike as callback.
setTimeout(() => {
console.log(“Display text message after 3 second delay”);
}, 3000);
remember.
Here Arrow passes the function directly to setTimeout, and the text information is set after the given delay time.
Summary of Anonymous functions, function expressions, and callbacks
| Function Concept | Function Description | With Example |
| Anonymous Functions | Anonymous Functions used without names, often used in expressions or as callbacks for any JavaScript program. | let message = function() { console.log(“Vcanhelpsu”); }; |
| Function Expressions | Functions expression defined within expressions and assigned to variables. They can be anonymous or named in program. | let add = function(p, q) { return p + q; }; |
| Callbacks | Callbacks Functions passed as arguments to other functions to be executed later in active JavaScript program. | setTimeout(() => { console.log(“Complete!”); }, 3000); |
Conclusion of Anonymous function in JavaScript.
- Anonymous functions in JavaScript programming are program functions without a name, and often these are used in JavaScript as inline or callback in function expressions.
- Where function expressions assign variables as functions, and these functions can be anonymous or named declared in the program. They are not hoisted in the program.
- Callbacks in a program are functions declared to be passed to other functions, which are executed later in the program as needed, often used in asynchronous operations in JavaScript programs.
