javascript - 如何在JavaScript中检查“未定义”？ [重复](How to check for “undefined” in JavaScript? [duplicate])

Question

This question already has an answer here:

(这个问题已经在这里有了答案：)

• Detecting an undefined object property 42 answers

  (检测未定义的对象属性 42个答案)

• How to check a not-defined variable in JavaScript 14 answers

  (如何检查JavaScript中未定义的变量 14答案)

• How to handle 'undefined' in javascript [duplicate] 3 answers

  (如何处理javascript中的“ undefined” [重复] 3个答案)

• how to check if a variable exist in javascript?

  (如何检查JavaScript中是否存在变量？)

  8 answers

  (8个答案)

What is the most appropriate way to test if a variable is undefined in JavaScript?

(测试JavaScript中是否未定义变量的最合适方法是什么？)

I've seen several possible ways:

(我已经看到了几种可能的方法：)

if (window.myVariable)

Or

(要么)

if (typeof(myVariable) != "undefined")

Or

(要么)

if (myVariable) //This throws an error if undefined. Should this be in Try/Catch?

  ask by goodguys_activate translate from so