Function Parameters and Arguments

A JavaScript function does not perform any checking on parameter values (arguments).

Earlier in this tutorial, you learned that functions can have parameters:

function functionName(parameter1, parameter2, parameter3) {
// code to be executed
}

Function parameters are the names listed in the function definition.

Function 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 passed arguments.

JavaScript functions do not check the number of arguments received.

If a function is called with missing arguments (less than declared), the missing values are set to undefined.

Sometimes this is acceptable, but sometimes it is better to assign a default value to the parameter:

function myFunction(x, y) {
if (y === undefined) {
y = 2;
}
}

Try it now

ECMAScript 2015 allows default parameter values in the function declaration:

function (x, y = 2) {
// function code
}

Try it now

Practice Excercise Practice now