JavaScript.The.Good.Parts reading notes (i) false value and = = operator _javascript Tips

the fake values for JavaScript are listed below,

Value	type
0	Number
NaN ( non-numeric )	Number
' ( empty string )	String
False	Boolean
Null	Object
Undefined	Undefined

The above values are false values as a criterion, such as:

Copy Code code as follows:

if (undefined) {
Alert (' undefined '); This line of code does not execute
}
while (null)
{
Alert (' null '); This line of code does not execute
}

Although all of these values are equivalent to false, they are not interchangeable.
Some examples are listed below:
undefined = = NULL//false
undefined = = NULL//true

Even
Nan = = Nan//false
Nan = = Nan//false
Ps:nan and Nan are not equal in either operation, isNaN (Nan) can be used to solve the problem of Nan's judgment.

the = = = (!=) operator enforces type conversions, and the conversion rules are quite bizarre. Here are some examples.

Copy Code code as follows:

' = = ' 0 '//False
0 = = ""/True
0 = ' 0 '/True
False = = ' false '//False
false = = ' 0 '/True
false = = undefined//False
false = = NULL//False
NULL = = undefined//True
' \t\r\n ' = 0//True

We recommend using the = = = = (!===) operator.