How TO - Set Default Parameters

Learn how to set default parameter values for JavaScript functions.

Default Parameters

If a function in JavaScript 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;
}
}

ECMAScript 2015 allows default parameter values in the function declaration:

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

Read more about functions in our JavaScript Function Tutorial.