JavaScript.The.Good.Parts Reading Notes (1) False Values ​​and === Operator_Javascript Skills

JavaScript的假值列表如下，

 

值	类型
0	Number
NaN (非数字)	Number
'' (空字符串)	String
false	Boolean
null	Object
undefined	Undefined

The above values ​​are used as judgment conditions and will be false values, such as:

Copy code The code is as follows:

if(undefined) {
alert('undefined' ); //This line of code will not be executed
}
while(null)
{
alert('null'); //This line of code will not be executed
}

While these values ​​are all equivalent to false, they are not interchangeable.
List some examples below:
undefined === null //false
undefined == null //true

Even
NaN === NaN //false
NaN == NaN //false
PS: NaN and NaN are not equal no matter which operation is used. IsNaN(NaN) can be used to solve the NaN judgment problem. The

==(!=) operator will perform forced type conversion, and the conversion rules are quite weird. Here are some examples.

Copy code The code is as follows:

'' == '0' // false
0 == '' // true
0 == '0' // true
false == 'false' // false
false == '0' // true
false = = undefined // false
false == null // false
null == undefined // true
' trn ' == 0 // true

Recommended to use == =(!===) operator.