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Parameters (Function Input) Parameters allow you to pass (send) values to a function. Parameters are listed inside the parentheses in the function definition.
Example function multiply(a, b) {
return a * b;
}
let result = multiply(4, 5);A function can have one parameter.
Examples function sayHello(name) {
return "Hello " + name;
}
let greeting = sayHello("John");
function toCelsius(fahrenheit) {
return (5 / 9) * (fahrenheit - 32);
}
let value = toCelsius(77);You can add as many parameters as you want, separated by commas.
Example function fullName(firstName, lastName) {
return firstName + " " + lastName;
}
let name = fullName("John", "Doe");Parameters vs. Arguments In JavaScript, function parameters and arguments are distinct concepts: Parameters are the names listed in the function definition. Arguments are the real values passed to, and received by the function.
JavaScript function definitions do not specify data types for parameters. JavaScript functions do not perform type checking on the arguments. JavaScript functions do not check the number of arguments received.
Accessing a function with an incorrect parameter can return an incorrect answer:
Example function toCelsius(fahrenheit) {
return (5/9) * (fahrenheit-32);
}
let value = toCelsius();ECMAScript 2015 allows function parameters to have default values. The default value is used if no argument is provided.
Formula
If y is not passed or undefined, then y = 10.function myFunction(x, y = 10) {
return x + y;
}
myFunction(5);A function can return a value back to the code that called it The return statement is used to return a value from a function