JS determines whether the variable is null and jsnull determines whether it is null.

JS determines whether the variable is null and jsnull determines whether it is null.

/*** Determine whether null * @ param data */function isNull (data) {return (data = "" | data = undefined | data = null )? "None": data ;}

Js judge whether the value is null

<Input type = "text" id = "name" value = "click" onclick = "checkNull ()"/>

<Script>
Function checkNull (){
Var name = document. getElementById ("name"). value. replace (/[]/g, ""); // remove all spaces
If (name. length = 0 | name = "click "){
Alert ("Enter data! ");
}
}
</Script>

Differences between variables = null and variables = ''in JS

The three are different.
Undefined
Declare a variable without a value. The default value is undefined.
For example:
Var I;

Null
Value assigned to a variable if you want to indicate that a variable has no specific value
Null can also be regarded as a value, like true or false.
For example:
Var I = null;

''
Null String
It can be considered as a special character that is the same as a and B.

Note:
Undefined = null; // return true
Undefined = null; // return false