Javascript 简写语法解释

Question

I gone through this syntax in my project. Can I get the explanation for this code please?

 // Handles focus on error title.
 var error = $('#consentError')[0];
 error && error.focus();

Is this the shorthand syntax for if() condition.

Answer 1

Yes, the code is equivalent to

var error = $('#consentError')[0];
if (error) {
  error.focus();
}

The if version is definitely easier to read and comprehend at a glance. Using the && method creates an unused expression, which is weird and is often forbidden by linters.

But jQuery has an even better way to achieve this - just call focus on the jQuery collection, and it'll call .focus() on the native element, if there is such an element (and if there isn't one, it just won't do anything - it won't throw).

$('#consentError').focus();