eslint for redundant double如何更改为有效

Question

I try to submit the following code

if(!!obj){

...

}

redundant double error , how can I fix it ? why I getting it now ...

Answer 1

ESLint is giving you the warning as the !! is redundant.

An if condition will coerce the condition into a boolean anyway, as an if condition is either true or false. So what you end up telling the javascript engine to do is, coerce to a boolean true / false, then not the value, and then not the value again, only to get the original coerced value.

But saying all this a double !, is not always redundant. For example say your storing data inside an object, and say you want to force a boolean storage, you could !!value it.

Sometimes I even use this just to double check what true / false something returns from the console.. eg. !!'' = false were as !!'0' = true and !!0 = false etc..