According to the teacher talked about as well as online bigwigs explained tidied
Null：
js keywords is null, null values represent, null can be seen as a special object of value, if an object is null, indicating that the object is not a valid object.
Undefined:
The following situation will return undefined:
1. Use of an undefined variable; var i;
2. Use a variable is defined but not declared;
3. Use of an object property, but the property does not exist or is not assigned;
4. When the call function, the provider does not provide the parameters:
function func(a){
console.log(a);
}
func();//undefined
5) When the function does not return a value, default return undefined
var a = func ();
a;//undefined
Difference between the two:
1. not the same type:
console.log(typeOf undefined);
//undefined
console.log(typeOf
null
);
//object
2. converted to different values: undefined is NaN, null 0
console.log(Number(undefined));
//NaN
console.log(Number(10+undefined));
//NaN
console.log(Number(
null
));
//0
console.log(Number(10+
null
));
//10
3.undefined===null;//false
undefined==null;//true
Null：
js keywords is null, null values represent, null can be seen as a special object of value, if an object is null, indicating that the object is not a valid object.
Undefined:
The following situation will return undefined:
1. Use of an undefined variable; var i;
2. Use a variable is defined but not declared;
3. Use of an object property, but the property does not exist or is not assigned;
4. When the call function, the provider does not provide the parameters:
function func(a){
console.log(a);
}
func();//undefined
5) When the function does not return a value, default return undefined
var a = func ();
a;//undefined
Difference between the two:
1. not the same type:
console.log(typeOf undefined);
//undefined
console.log(typeOf
null
);
//object
2. converted to different values: undefined is NaN, null 0
console.log(Number(undefined));
//NaN
console.log(Number(10+undefined));
//NaN
console.log(Number(
null
));
//0
console.log(Number(10+
null
));
//10
3.undefined===null;//false
undefined==null;//true