Whats the difference in checking for falsy / truthy values in different ways?

Question

When working in JavaScript / Typescript, often times occur when i need to check a length exists or if a value is true or false.

The main question is, is there any difference in performance or behaviour between checking as follows...

const data = ['hello', 'good', 'day'];
(data.length) // true 
(data.length > 0) // also true

much like

const booleanValue = false;
(!booleanValue) // true 
(booleanValue === false)  //also true

is there a best way to do this or does it all boil down to readability.

Readability; the difference is negligible. If you need to optimise at this level, profiling beats assumptions, always (and what's fastest changes with engine type and version, as they too get optimised,) — Amadan, Nov 27 '18 at 08:36
Have a look at this: https://softwareengineering.stackexchange.com/questions/12807/make-a-big-deal-out-of-true — Mariyan, Nov 27 '18 at 08:39
*When you have a boolean value*, `!value` means exactly the same thing as `value === false` in JavaScript, so this applies: https://stackoverflow.com/questions/11831881/if-boolean-false-vs-if-boolean/11831904#11831904 — Ry-, Nov 27 '18 at 08:40
Similarly, *when you have an array* and are *also using its length in a boolean context*, `value.length` and `value.length > 0` mean the same thing. But it’s easy to return the wrong type of value, e.g. if you write expressions like `data.length && data[0]` – that entire `&&` expression evaluates to `0` when the array is empty, not `false`. Better to be explicit with the types of your expressions IMO. — Ry-, Nov 27 '18 at 08:44

score 3 · Accepted Answer · answered Nov 27 '18 at 08:40

There are differences depending on what you want to achieve ...

for example:

0 == false // true
0 === false // false
undefined == null // true
undefined === null // false
...

Here is a game that will help you understand what are the Boolean relationships in JS: Pedagogical-Game

1 Answers1