Use Default Parameters

Default parameters allow providing default values for function parameters. These default values are used if nothing or undefined is passed into the function. For example, function f(p = 42) { ... } sets p to 42 if no value is passed in.

Previous ways of setting default values, for example p = p || 42 can be converted to default parameters. This refactoring supports converting the following expressions and variants of them:

• or assignment, e.g. p = p || 42 or p ||= 42
• nullish coalescing operator, e.g. p = p ?? 42
• ternary with falsy check on parameter, e.g. p = p ? p : 42
• ternary with null check, e.g. p = p == null ? 42 : p or p = p != null ? p : 42
• ternary with undefined check, e.g. p = p === undefined ? 42 : p
• ternary with typeof check, e.g. p = typeof p === "undefined" ? 42 : p

Learn More: Default Parameters (MDN)

function example(x) {
    x = x == null ? "default" : x;
    console.log(x);
}

example(null); // prints "default"

function example(x = "default") {
    console.log(x);
}

example(null); // prints "null"

Original Code

Changes

Transformed Code

function x(p = 42) {
  console.log(p);
}