javascript - 检测未定义的对象属性(Detecting an undefined object property)

Question

检查JavaScript中的对象属性是否未定义的最佳方法是什么？

  ask by Matt Sheppard translate from so

Answer 1

Use:

(采用：)

if (typeof something === "undefined") {
    alert("something is undefined");
}

If an object variable which have some properties you can use same thing like this:

(如果对象变量具有某些属性，则可以使用类似的方法：)

if (typeof my_obj.someproperties === "undefined"){
    console.log('the property is not available...'); // print into console
}