JavaScript private variable usage

The principle of private instance variables is based on the scope. Private instance variables are implemented using the var keyword in JavaScript Functions and only valid within functions.

If you have been familiar with other languages, you should have been familiar with the concept of private variables. Private is not protected and cannot be modified or accessed. It can only be accessed and modified through the APIS you provide. However, there is no private variable in JavaScript. All members can access and modify it by subscript, for example:

Private variable

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Var F = function (){}; F. prototype. name = "zhangsan "; Var a = new F (); Alert (a. name); // zhangsan A. name = "lisi "; Alert (a. name); // lisi

In JavaScript, the instance member variables are easily modified and deleted. A lot of people do this.

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Var F = function (){}; // Underline the variable F. prototype. _ name = "zhangsan "; Var a = new F (); // Access is the same as normal access Alert (a. _ name); // zhangsan // It can be easily modified. A. _ name = "lisi "; Alert (a. _ name); // lisi

It seems that it is common to underline the bit private variables. However, this is only a default convention. In fact, using JavaScript features, we can define private variables as follows:

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(Function (window ){ // Define the default value of the private variable Var name = "zhangsan "; Var F = function (){}; // Access private variables F. prototype. getName = function (){ Return name; }; // Update private variables F. prototype. setName = function (str ){ Name = str; }; Window. F = F; }) (Window ); Var a = new F (); A. getName (); // zhangsan A. setName ("lisi "); A. getName (); // lisi

This is also the most widely used method.

Private Static variables

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<Script language = "javascript" type = "text/javascript"> Var JSClass = (function (){ Var privateStaticVariable = "nowamagic "; Var privateStaticMethod = function (){ Alert ("nowamagic "); }; Return function (){ This. test1 = function (){ Return privateStaticVariable; } This. test2 = function (obj ){ PrivateStaticVariable = obj; } This. test3 = function (){ PrivateStaticMethod (); } }; })(); Var testObject1 = new JSClass (); Var testObject2 = new JSClass (); Alert (testObject1.test1 ()); TestObject1.test2 ("change nowamagic "); Alert (testObject2.test1 ()); TestObject2.test3 (); </Script>

Dynamic generation of private variable accessors

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// Create a new user object and accept an object with many attributes as a parameter Function User (properties) { // Traverse all attributes of the object and ensure that its scope is correct For (var I in properties ){ (Function (which ){ Var p = I; // Create a new reader (getter) for this attribute) Which ["get" + p] = function (){ Return properties [p]; }; // Create a new setter for this attribute) Which ["set" + p] = function (val) { Properties [p] = val; }; }) (This ); } } // Create a new user object instance and pass an object with two attributes as a parameter Var user = new User ({name: "Bob", age: 44 }); // Read the attribute value Alert (user. getname ()); // Set the attribute value User. setage (23 );