When deciding on which code style to use, under different circumstances (i.e. number of parameters, return value, etc.) a good solid rule for consistency and terseness is: Always use the minimum required syntax for the situation
The minimum does not include variable/parameter names, which should should be semantic to the meaning or general depending on how the function will be used. Using an unused parameter name to save one char (like _ => 2*2) is confusing and should be avoided.
With this rule in mind we end up with this:
// no params
() => {} // "noop" no parameters, no operations, no return value
() => value + 1 // no parameters, one line operation, a return value (that is not an object)
() => ({ foo: 'bar' }) // no parameters, one line operation, a object return value
() => { // no parameters, multi-line operation, a return value/object
//...
return value;
}
// one param
num => {} // "wtf" one parameter, no operations, no return value
num => num * num // one parameter, one line operation, a return value (that is not an object)
text => ({ value: text }) // one parameter, one line operation, a object return value
items => { // one parameter, multi-line operation, a return value/object
//...
return newItems;
}
// multiple params
(item, collection) => {} // "seriously wtf" multiple parameters, no operations, no return value
(n, col) => col.indexOf(n) // multiple parameters, one line operation, a return value (that is not an object)
(val, type) => ({ type, val }) // multiple parameters, one line operation, a object return value
(items, comparetor) => { // multiple parameters, multi-line operation, a return value/object
//...
return newItems;
}This may look inconsistant at first glance, but is consistant when applied consistently and leads to easy to read/understand code.