How to inherit and use non-function objects in Javascript

This article provides some detailed descriptions and examples of the inheritance and usage of non-function objects in Javascript. There are two types of Javascript inheritance. One is inheritance based on \ "function object \", that is, a function inherits another function.

The other is inheritance based on "non-function objects" and does not involve functions. Its approach is completely different from the previous case.

1. What is the inheritance of "non-function objects?

For example, there is an object called "Chinese ".

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Var Chinese = { Nation: 'China' }; Another object is called "Doctor ". Var Doctor = { Career: 'docker' }

How can I enable "doctor" to inherit "Chinese"? That is to say, how can I generate a "Chinese doctor" object?

Ii. object () method

Douglas Crockford, inventor of json format, proposed an object () function to achieve this.

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Function object (o ){ Function F (){} F. prototype = o; Return new F (); }

This object () function is actually only used to direct the prototype attribute of the Child object to the parent object so that the child object can be connected with the parent object.

When used, the first step is to generate sub-Objects Based on the parent object:

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Var Doctor = object (Chinese );

Then, add the attributes of the sub-object:

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Doctor. career = 'Doc ';

At this time, the sub-object has inherited the attributes of the parent object.

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Alert (Doctor. nation); // China

Iii. Shallow copy

In addition to the prototype chain, there is another idea: copying all attributes of the parent object to the sub-object can also realize inheritance.

The following function is used for copying:

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Function extendCopy (p ){ Var c = {}; For (var I in p ){ C [I] = p [I]; } C. uber = p; Return c; }

Write as follows:

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Var Doctor = extendCopy (Chinese ); Doctor. career = 'Doc '; Alert (Doctor. nation); // China

However, there is a problem with such a copy. That is, if the attribute of the parent object is equal to an array or another object, in fact, the sub-object only obtains a memory address rather than a real copy, so there is a possibility that the parent object will be tampered.

Now, add a "Birthplace" attribute to Chinese. Its value is an array.

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Chinese. birthPlaces = ['beijing', 'shanghai', 'Hong Kong '];

Using the extendCopy () function, Doctor inherits Chinese.

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Var Doctor = extendCopy (Chinese );

Then, we add a city for Doctor's "Birthplace:

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Doctor. birthPlaces. push ('xiamen ');

What happened? The Chinese "Birthplace" has also been changed!

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Alert (Doctor. birthPlaces); // Beijing, Shanghai, Hong Kong, Xiamen Alert (Chinese. birthPlaces); // Beijing, Shanghai, Hong Kong, Xiamen

Therefore, extendCopy () is just a copy of the basic type of data. We call this copy "shortest copy ". This is an early Method for jQuery to implement inheritance.

Iv. Deep copy

The so-called "Deep copy" means to copy arrays and objects in the true sense. Its implementation is not difficult, as long as the recursive call of "shortest copy.

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Function deepCopy (p, c ){ Var c = c || {}; For (var I in p ){ If (typeof p [I] === 'object '){ C [I] = (p [I]. constructor = Array )? []: {}; DeepCopy (p [I], c [I]); } Else { C [I] = p [I]; } } Return c; }

Write as follows:

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Var Doctor = deepCopy (Chinese );

Now, add an attribute to the parent object and the value is an array. Then, modify this attribute on the sub-object:

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Chinese. birthPlaces = ['beijing', 'shanghai', 'Hong Kong ']; Doctor. birthPlaces. push ('xiamen ');

In this case, the parent object will not be affected.

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Alert (Doctor. birthPlaces); // Beijing, Shanghai, Hong Kong, Xiamen Alert (Chinese. birthPlaces); // Beijing, Shanghai, Hong Kong

Currently, the jQuery library uses this inheritance method.