JavaScript. The. Good. Parts Reading Notes (1) dummy value and = Operator

JavaScriptThe list of false values is as follows,

 

Value	Type
0	Number
NaN (Non-numeric)	Number
''(Null String)	String
False	Boolean
Null	Object
Undefined	Undefined

The above values will all be false values as judgment conditions, such:

Copy codeThe 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
}


Although all these values are equivalent to false, they are not interchangeable.
The following are some examples:
Undefined === null // false
Undefined = null // true

Even
NaN = NaN // false
NaN = NaN // false
PS: NaN and NaN are not equal to each other. You can use IsNaN (NaN) to solve the NaN judgment problem.

= (! =) The operator performs forced type conversion, and the conversion rules are quite strange. The following are some examples.
Copy codeThe 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
'\ T \ r \ n' = 0 // true

We recommend that you use = (! =) Operator.