Default parameter values allow callers to specify as many or as few arguments as they want while getting the same functionality and minimizing
boilerplate, wrapper code, making a function easier to use.
All function parameters with default values should be declared after the function parameters without default values. Otherwise, it makes it
impossible for callers to take advantage of defaults; they must re-specify the defaulted values or pass undefined to be able to specify
the non-default parameters.
function multiply(a = 1, b) { // Noncompliant: parameter with default value should be last
return a*b;
}
let x = multiply(1, 42); // Cannot benefit from default value
Reorder the function parameters so that the ones with default values come after the ones without default values.
function multiply(b, a = 1) {
return a*b;
}
let x = multiply(42);
Exceptions
When writing Redux reducers, there is a convention to use default argument syntax to provide initial state (first argument), while action (second
argument) is mandatory. A reducer may be called with undefined as the state value when the application is being initialized.
// Use the initialState as a default value
export default function appReducer(state = initialState, action) {
switch (action.type) {
default:
return state;
}
}
