JavaScript must know (six) delete in instanceof

in

in Determine whether the string on the left or the attribute that can be converted into a string belongs to the right.

 var data = { x: , y: };//Define the direct object alert("x" in data);//true , x is an attribute alert( in data);//false , which is the attribute value of data. var arr = [, , ];//Defines the direct array object alert( in arr);//true ,arr The index of the array includes,, is one of its [] attributes. alert( in arr);//false, not its attribute.

instanceof

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

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

delete delete

delete delete the attributes of an object

 var o = { x: , y: };alert(delete ox); //true Delete successfully alert("x" in o);//false x is not an attribute of o var o = ;alert(delete this.o);//falsey = ;alert(delete this.y);//truealert(delete this.window);//false

Summary

delete is a unary operator. delete cannot delete built-in global variables in JavaScript, nor can it delete global variables declared by var, but it can delete global variables that are not declared by var.

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