Question

我想要建立的是：一个类Log，它有一个全局变量_level，表示当前的日志级别。一个函数日志（level，msg），它将级别与_level进行比较，并决定是否打印msg。

用法如下：

Log.SetLevel(1);  //global level
var logger1 = new Log();
logger1.log(0, "should print");
logger1.log(2, "should not print");

但是我无法完成它，似乎我对Javascript对象模型的理解存在一些问题，有人可以附上一个简单的代码吗？

Answer 1

这应该有效：

function Log() {}
Log._level = Infinity; // Log all messages by default

Log.SetLevel = function (level) {
  Log._level = level;
};

Log.prototype = {
  log: function (level, message) {
    if (level <= Log._level) {
      console.log(message);
    }
  }
};

演示：

var logger1 = new Log();

logger1.log(0, "should print");
logger1.log(1, "should print");
logger1.log(2, "should print");

Log.SetLevel(1);  //global level

logger1.log(0, "should print");
logger1.log(1, "should print");
logger1.log(2, "should not print");

Answer 2

Javascript没有＆＃34;类＆＃34; ，但是，你可以创建一个构造函数并按照这样做

// create constructor
function Log() {}

// "global" Log level
Log.prototype.level = 0;

// Logger method
Log.prototype.log = function (level, message) {
    return level === this.level ? alert(message) : false;
};

// change level method
Log.prototype.setLevel = function(level) {
    // change level on constructor prototype
    return this.constructor.prototype.level = level;
};

这是完成此操作的正确方法

var logger = new Log;
logger.setLevel(1)
logger.log(1, "should print");
logger.log(2, "should not print");

这样你也可以实际访问关卡，你不应该不必要地隐藏事物

Answer 3

您可以执行以下操作，以保持＆＃34; global＆＃34;闭包中的 level ，并提供访问它的特权函数。

// Initialise the constructor
var Log = (function() {

  // Keep level private in a closure
  var _level = 0;

  // Actual constructor function (it can be called anything)
  function Log(){

    /* constructor code here */

  }

  // Priviliged method to set the value of level
  Log.setLevel = function(level) {
    _level = level;
  }

  // Priviliged method to get the value of level
  Log.getLevel = function() {
    return _level;
  }

  // Assign Log to global variable Log
  return Log;
}());

// Method inherited by all instances of Log
Log.prototype.log = function(level, msg) {
  if (level <= Log.getLevel()) {
    console.log(msg);
  }
}

// Create some instances
var logger0 = new Log();
var logger1 = new Log();

// Set the level
Log.setLevel(1);

// Do some logging
logger0.log(1, 'should print 0');     // prints
logger0.log(2, 'should not print 0'); // doesn't print
logger1.log(1, 'should print 1');     // prints
logger1.log(2, 'should not print 1'); // doesn't print

console.log(Log.getLevel()); // 1

Answer 4

您需要编写代码：

var logLevel = 1;

function Log() {
    this.log = function (level, msg) {
        if (level === logLevel) {
            alert(msg);
        }
        else {
           //Whatever you want to do
        }
    };
}

var logger1 = new Log();
logger1.log(1, "should print");    //will alert
logger1.log(2, "should not print");    //will not alert
alert(logLevel);        //to prove that 'logLevel' is defined at a global level. The value is alerted signifying its scope to be at the global level

您可以在此处看到：http://jsfiddle.net/4f34c/1/

希望这有帮助!!!

如何创建Javascript类方法和类Consts？

4 个答案: