Simple method to determine if a JavaScript object is null or the attribute is empty_javascript skills

First let’s talk about the difference between null and undefined:

Executing typeof on declared but uninitialized and undeclared variables will return "undefined".

null represents a null object pointer, and the typeof operation will return "object".

Generally, the value of a variable is not explicitly set to undefined, but on the contrary, for a variable that will save an object, the variable should be explicitly allowed to save the null value.

var bj;
alert(bj); //"undefined"
bj = null;
alert(typeof bj); //"object"
alert(bj == null); //true
bj = {};
alert(bj == null); //false

The following two functions were given to me by Senior Brother Deng, thank you.

/*
* 检测对象是否是空对象(不包含任何可读属性)。
* 方法既检测对象本身的属性，也检测从原型继承的属性(因此没有使hasOwnProperty)。
*/
function isEmpty(obj)
{
for (var name in obj)
{
return false;
}
return true;
};

The empty object mentioned here is {} or null. I wrote a test case.

var a = {};
a.name = 'realwall';
console.log(isEmpty(a)); //false
console.log(isEmpty({})); //true
console.log(isEmpty(null)); //true

//注意参数为null时无语法错误哦，即虽然不能对null空指针对象添加属性，但可以使用for in 语句

　　
?
/*
* 检测对象是否是空对象(不包含任何可读属性)。
* 方法只既检测对象本身的属性，不检测从原型继承的属性。
*/
function isOwnEmpty(obj)
{
for(var name in obj)
{
if(obj.hasOwnProperty(name))
{
return false;
}
}
return true;
};

The difference between

{} and null:

This thing is very important.

var a = {};
var b = null;

a.name = 'realwall';
b.name = 'jim'; //这里会报错，b为空指针对象，不能像普通对象一样直接添加属性。
b = a;
b.name = 'jim'; //此时 a 和 b 指向同一个对象。a.name, b.name 均为'jam'