正确使用以下语句性能的正确方法是哪种？

Question

Which approach is most recommended. First or Second ?

var x = document.querySelectorAll("span");

// #1:  Console returns false
x.length > 0 && x[0].blur();

// #2:  Console returns undefined
if (x.length > 0) {
  x[0].blur();
}

Answer 1

If you find x.length > 0 then you will definitely get x[0] and do not need to check && x[0].blur(); . So your second approach is much better.

if (x.length > 0) {
  x[0].blur();
}