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Default parameters

Default parameters in JavaScript programming allow programmers to display default values ​​for declared function parameter arguments. If the declared function is called in the current program without any particular argument for a parameter, then the default function accesses the parameter argument value. Declare default parameters in a function is special in JavaScript programs when the programmer wants to ensure that the parameter in the currently declared function always has a valid access value, the program first checks whether the parameter value is given or not.

Syntax of JavaScript function default parameter.

function functionName(parameter1 = defaultValue0, parameter1 = defaultValue0) {

/ Program code to be executed with default parameter argument

}

Description of JavaScript function default parameter.

• Remember, if no parameter value is provided while calling the current function, then it will hold the declared value in default value.
• If a parameter value is provided in a function, it will hold the value provided, and the existing default value will be ignored.

Example of JavaScript default parameter.

Example of function with default value.

function message(company = “Vcanhelpsu”) {

console.log(“Get best informatin technolgy resources at, ” + company + “.”);

}

message(“Vandevelop”); // Result – Get best informatin technolgy resources at,Vandevelop

message(); // Result – Get best informatin technolgy resources at,Vcanhelpsu

Explanation of function with default value parameter.

In this function the default value of parameter company is “Vcanhelpsu”. If message() is called without any argument, it uses “Vcanhelpsu” as the company.

Multiple parameters with default values ​​​​in JavaScript.

function countrate(rate, taxRate = 0.7, rebeat = 1) {

const tax = rate * taxRate;

const endrate = rate + tax – rebeat;

return endrate;

}

console.log(countrate(200, 0.20, 8)); // Result is – 232

console.log(countrate(200)); // Result is – 339 (here default taxRate – 0.7 and discount – 1)

Explanation of multiple parameters with default values.

In this program, taxRate is declared as 0.7 (70%) by default and discount is declared as 1 by default. If no value is provided, the function uses the default value.

Default parameters with expressions in JavaScript.

JavaScript programmers can apply function expressions to default declared parameter. These expressions are evolved as soon as these functions are called in the program.

function companydetail(companyName, services = companyName) {

console.log(companyName + ” , ” + services);

}

companydetail(“Vcanhelpsu”, “Computer programming”); // Result is – Vcanhelpsu, Computer programming

companydetail(“Explore Programming Resources”); // Result is – Explore Programming Resources, Explore Programming Resources

Explanation of default parameters with expressions in JavaScript.

Here in this condition, if the services type is not indicated, then it defaults to the value of companyName. Due to this, if only one companyName is passed to the function, then it will repeat it.

Undefined default parameters in JavaScript.

Default values ​​in JavaScript function programs are used only when the function parameter is undefined. If you pass null or any other value to a function, then the program does not use the function default value.

function message(companyname = “Vcanhelpsu”) {

console.log(“Join Course, ” + companyname + “.”);

}

message(); // Result – Join Course, Vcanhelpsu.

message(“Harry”); // Result – Join Course, Harry.

message(null); // Result – Join Course, null.

Expansion of undefined default parameters in JavaScript.

In this function null is passed in clear order, here null is treated as a value, not undefined, due to this it does not use default parameters in the function.

Use of function as default parameter in JavaScript.

JavaScript programmers can also apply functions or more complex expressions in order of default values.

function createemployee(employeename, prefix = “employee – “) {

return prefix + employeename;

}

console.log(createemployee(“Bhavishi”)); // Result – employee – Bhavishi

console.log(createemployee(“Lalit”, “founder – “)); // Result – founder – Lalit

Explanation of using functions as default parameters in JavaScript.

Here the default value of prefix parameter is “employee -“, but if programmer provides any other value (like “founder -“) then it will override the default function value in the program.

Benefits of using default parameters in JavaScript.

Cleaner program source code.

Using default parameter in JavaScript programs eliminates the need for programmers to manually check whether a parameter value has been passed to the current function and if not, provides a default value to the function. This makes your function program cleaner and more readable.

// Function program without default parameters.

function message(companyname) {

if (companyname === undefined) {

companyname = “Vanhelpsu”;

}

console.log(“Programming, ” + companyname + “.”);

}

// Function program with default parameters.

function message(companyname = “Vcanhelpsu”) {

console.log(“Programming, ” + companyname + “.”);

}

Better program control over function Behaviors.

Default function parameters in JavaScript provide programmers better control over how a function behaves when a function argument is missing. This prevents programming errors caused by undefined values ​​in a function program.

Better flexibility in function usage.

Allowing optional parameters in a function program with meaningful default values ​​makes functions more flexible, making it easier to use an existing function in multiple contexts.

Default Parameter vs. Arguments Object in JavaScript.

Before the use of default parameter in ES6 in JavaScript programming, JavaScript software developers often used arguments objects to manage missing program parameter arguments and indicate default values ​​manually. But, with default function parameters, it becomes easier and more readable.

Using Arguments in JavaScript Old Method Example.

function message(companyname) {

if (arguments.length === 0) {

companyname = “Vcanhelpsu”;

}

console.log(“Welcome to, ” + companyname + “.”);

}

message(); // Result – Welcome to, Vcanhelpsu

JavaScript Example of New Method Using Default Parameters.

function message(companyname = “vcanhelpsu”) {

console.log(“welcome to, ” + companyname + “.”);

}

message(); // Result – welcome to,vcanhelpsu

Explanation of New Method Parameters.

The new syntax with default parameters in JavaScript programming is more detailed and easy to understand than program arguments.

Default Parameters Important Notes.

• Evaluation of default parameter in the program – Evaluation of default values ​​in the program is done only if the argument is not provided in the program or the argument is explicitly defined as undefined. If you pass a null value to the function, it does not use the default value in the current function.
• Order of parameters in the program – Default program parameters should be displayed at the bottom of the parameter list to avoid any kind of program ambiguity. Where programmers can display program parameters with default values ​​after parameters that do not have default parameter values.

// Correct function parameter syntax.

function sample(parameter1, parameter2 = “default”) {}

// Incorrect function parameter syntax error.

function sample(parameter1 = “default”, parameter2) {}

javascript Default Parameter Summary

Conclusion of Default Parameters.

Default parameter in JavaScript programming are a powerful modular functional programming feature that allows JavaScript programmers to define default values ​​for function parameter, eliminating the need for manual function condition checking or conditional assignment. This makes the functions in your program more flexible and readable.