是var db = window.openDatabase && openDatabase（）; 避免错误的好方法？

Question

Is this a good way to avoid errors?

var sql_db = window.openDatabase && openDatabase('table', '1.0', 'description', 4096);

It seems to work, but is this a good way to avoid errors if a feature isn't implemented? Later on I'll just check if sql_db is undefined / null / false .

Does it work in all browsers, and does it return undefined , null or false if window.openDatabase isn't supported?

Please note that this isn't only about openDatabase but rather any feature that may not be implemented in all browsers. I'm already doing window.console && console.log() and that works fine, but in that case I'm not saving any object to a variable.

Answer 1

Yes, that's fine, although I'd suggest adding the window. part after the && as well, just to prevent conflict with any local variables.

If the global variable is not defined, it will return undefined - this behaviour is consistent across browsers, however keep in mind that undefined is not a reserved word and can theoretically be overwritten. Why someone would do that is beyond me, but it's good to know.

Answer 2

I'm not entirely convinced whether this is a good idea for this specific case.

For console && console.log , I think it's pretty good, but if you're using it with the openDatabase call then maybe not.

Why?

If you have a variable that you use for database calls, sql_db , what if it's null? It's going to cause an error. Are you going to prefix every single use with sql_db && ? It feels like a kludge and it might not even be possible to always do that.

In a case where you actually will be using the result of the call for something, you probably should just opt for a normal if-else check. This way you can detect the failure early, and the code which depends on the result of that will work more reliably without requiring boilerplate variable checks.