JSON 数组是否为空

Question

我有一个数组var st = { "itema":{...},"itemb":[{"id":"s01","cd":"c01","dd":"d01",....}{"id":"s02","cd":"c02","dd":"d02",....}]}如何检查 st 是否为空？

Answer 1

You can use Object.getOwnPropertyNames() to see whether there are any object properties:

if (Object.getOwnPropertyNames(st).length === 0) {
  // no properties
}

Now, if there are properties, it's up to you to decide whether an object with properties whose values are undefined or null is "empty" or not.

Another approach that might more closely reflect your concept of "empty" would be to stringify the object as JSON:

var __EMPTY = JSON.stringify({});
// ...
if (JSON.stringify(st) === __EMPTY) {
  // ...
}

Not the most efficient thing to do of course if your object might be relatively large in common cases.

The concept of an "empty object" really isn't very natural in JavaScript, at least in my experience.