I will never use || (OR) for default values

TL;DR;

I will never use || for default values, but default parameter.

For example, instead of

function sort(array, startIndex, endIndex) {
  startIndex = startIndex || 0;
  endIndex = endIndex || array.length — 1;
  ...
}

I would use,

function sort(array, startIndex = 0, endIndex = array.length - 1) {
  ...
}

Why?

I have been using || for default values, till date.

But it bite me big time. A quick sort implementation in JavaScript, fell in to infinite recursion, because of ||, when an already sorted array was passed.

Long story short, w.r.t the above quick sort implementation in JavaScript even if endIndex will be passed as 0 (zero), on purpose, it would be evaluated to array.length - 1. As 0 is a falsy value in JavaScript. Same would happen if '' or null, is passed as endIndex, or any other falsy values.

However the intention have been, if endIndex was not passed (undefined), then evaluate it to array.length — 1. Thus, modifying the condition to endIndex = endIndex === undefined ? length - 1 : endIndex;, resolves the issue.

ES2015 nakes it easier with default parameter.

With default parameters, the undefined checks in the function body is no longer necessary.

So, instead of

function sort(array, startIndex, endIndex) {
  startIndex = startIndex === undefined ? 0 : startIndex;
  endIndex = endIndex === undefined ? array.length — 1 : endIndex;
  ...
}

I would use,

function sort(array, startIndex = 0, endIndex = array.length - 1) {
  ...
}