JavaScript Function Parameters
Parameters (Function Input)
Parameters allow you to pass (send) values to a function.
Parameters are listed inside the parentheses in the function definition.
Functions with One Parameter
A function can have one parameter.
Examples
function sayHello(name) {
return "Hello " + name;
}
let greeting = sayHello("John");
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function toCelsius(fahrenheit) {
return (5 / 9) * (fahrenheit - 32);
}
let value = toCelsius(77);
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Functions with Multiple Parameters
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");
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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.
Parameter Rules
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.
Incorrect Parameters
Accessing a function with an incorrect parameter can return an incorrect answer:
Example
function toCelsius(fahrenheit) {
return (5/9) * (fahrenheit-32);
}
let value = toCelsius();
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Default Parameter Values
ECMAScript 2015 allows function parameters to have default values.
The default value is used if no argument is provided.
Example
If y is not passed or undefined, then y = 10.
function myFunction(x, y = 10) {
return x + y;
}
myFunction(5);
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