In JavaScript, null is an object. There's another value for things that don't exist, undefined . The DOM returns null for almost all cases ... ... <看更多>

How to check if a property exists in an object in JavaScript by using the hasOwnProperty() method, the in operator, and comparing with undefined. ... <看更多>

There's a lot of ways to do this. Here's an exotic (and costly) one: if(((json || {}).data || {}).formkeys !== void 0){}. ... <看更多>

From the example in the README <% if (user) { %> <%= user.name ... The same is actually true of undefined variables in regular JavaScript. ... <看更多>