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Encapsulation in JavaScript

JavaScript does not allow you to define a method as public or private. This is a limitation users need to get around to, because in real life you don't want to expose all methods as public method.

Here is a simple implementation of the case where you want to verify input code.

1function verifycode(code) {
2  console.log(code.length);
3  return code.length == 4 ? true : false;
4}
5
6function info(code) {
7  if (verifycode(code)) {
8    console.log(code + " is valid");
9  } else {
10    console.log(code + " is wrong");
11  }
12}
13
14info("abcd");
15info("rty");

In the above implementation anyone can call the method verifycode. Not good. Here is one way to fix this problem.

1var Lab = Lab || {};
2Lab = (function () {
3  var verifycode = function (code) {
4    console.log(code.length);
5    return code.length == 4 ? true : false;
6  };
7  return {
8    info: function (code) {
9      if (verifycode(code)) {
10        console.log(code + " is valid");
11      } else {
12        console.log(code + " is wrong");
13      }
14    },
15  };
16})();
17
18Lab.info("abcd");
19Lab.info("rty");
20Lab.verifycode("abcd"); //verifycode is private

Another way to solve the same problem would be to create a constructor function. Here is an implementation.

1function Lab(code) {
2  this.code = code;
3  var verifycode = function () {
4    return code.length == 4 ? true : false;
5  };
6  this.info = function () {
7    if (verifycode()) {
8      console.log(code + " is valid");
9    } else {
10      console.log(code + " is wrong");
11    }
12  };
13}
14new Lab("abcd").info();

Here is another way to solve the same problem. In this case I have moved all the public methods to prototype.

1function Lab(code) {
2  this.code = code;
3  this.verifycode = function () {
4    l = code.length;
5    return l == 4 ? true : false;
6  };
7}
8
9Lab.prototype.info = function () {
10  if (this.verifycode()) {
11    console.log(this.code + " is valid");
12  } else {
13    console.log(this.code + " is wrong");
14  }
15};
16
17new Lab("abcd").info();
Neeraj Singh in JavaScript
October 12, 2009
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