Enumeration For/in

The for/in loop iterates through all the properties that can be enumerated in the object, including its own and inherited properties. The built-in methods of object inheritance cannot be enumerated, and the property methods that are added to the object's own or inherited classes in code are enumerable, but the built-in properties of the object can be enumerated, not necessarily, For example, we can try math's built-in random property (not enumerable) and window's built-in Name property (enumerable).

I. The following summarizes some of the tool functions that enumerate object properties:

1. If O and P have the same name attribute, p overrides o

function Extend (o,p) {    for in  p) {        ifcontinue;   Masking Enumerable inherited properties        O[prop] = P[prop];    }     return o;}

2. If O and P have the same name attribute, p does not affect the O property

function Merge (o,p) {    for in  p) {        ifcontinue;   Masking an enumerable inherited property        ifcontinue;   property with the same name skipped        O[prop] = P[prop];    }     return o;}

3. If the O attribute does not have the same name attribute in P, delete the attribute in O

function Restrict (o,p) {    for (var . o) {        ifin  P) Delete O[prop];    }     return o;}

4. Delete the property with the same name in P in O

function Subtract (o,p) {    for (var in p) {        delete o[prop];    }     return o;}

Enumeration For/in