JavaScript must know of Six delete in instanceof

in

in determines whether the string on the left or what can be converted into a string belongs to the property on the right.

var data = { x: , y: };// Direct object defined 
alert("x" in data);//true ,x  yes data  Of 1 Attributes 
alert( in data);//false ,  yes data Property value of.  
var arr = [, , ];// A direct array object is defined 
alert( in arr);//true ,arr  Array index Include ,,,  It's his 1 individual [] Properties. 
alert( in arr);//false  Is not his property.  

instanceof

instanceof expects the instance on the left to be the type of object on the right.

var date = new Date();
alert(date instanceof Date);//true
alert(date instanceof Object);//true
alert(date instanceof Number);//false  　 
var date = [, , ];
alert(date instanceof Array);//true
alert(date instanceof Object);//true
alert(date instanceof Number);//false 

delete

delete Deletes Properties of an Object

var o = { x: , y: };
alert(delete o.x); //true  Delete succeeded 
alert("x" in o);//false x No o Properties of  
var o = ;
alert(delete this.o);//false
y = ;
alert(delete this.y);//true
alert(delete this.window);//false 

summary

delete is a unary operator. delete cannot delete global variables built into javascript or those declared by var, but it can delete global variables not declared by var.