优化条件/ if块，从性能角度来看，什么是更好的选择？

Question

I am writing a JS library, and there are two things that have been on my mind for quite some time though.

Consider an option:

var option = { bool : true } ;

Now, imagine I do either

if(option.bool) 

      or

if(option.bool === true) 

The first case, despite knowing for sure that it's either true or false , I imagine is the equivalent of:

var tmp = options.bool;
if ( tmp !== undefined && tmp !== null && ( tmp === true || tmp ... ) 

That means that to try the options.bool = true it has to check both undefined and not null, before testing for true.

Therefore the latter case should be more performant. However, the latter case, takes a considerably more characters and will lead to a larger lib, if repeated many times.

But maybe my understanding is incorrect.

Right now, even if I do:

var bool = window.t ? true : false; 

if ( bool === true ) // I still have to check for true to 'have the optmimal version'?

Maybe the last case can be optimized by the compiler, but when it's a global option I imagine it's different?

Please share with me your thoughts on this.

Answer 1

The answer is simple. It's less about coding patterns and more about logic. In this scenario there are always 3 possibilities and you need to cater for each of them. Ie. 1. TRUE 2. FALSE 3. undefined If the value is undefined then do you want it to fall under the true or false clause? OR should it be catered for differently?

Another important thing to remember is that if it is undefined then it will always execute the code in the false clause. Is that what you want?

If you know that the value will always be either true or false then I suggest that you still use the syntax == true as this is more readable. Someone browsing over the code would know that you are looking for the boolean value and not testing if the field has been set.

You have to think about these 3 cases every time you have a boolean in an if statement, so there is no 1 answer for you.