自定义 'use strict' 类指令

Question

我正在为我的项目寻找更好的 logging/debugging 方法。所以我想出了使用像 'use strict'.

这样的自定义指令的想法

能不能这样写

function xyz () {
   'loglevel: info';
   /// Some other code
   logging.debug("foobar");
}

如果 xyz 有指令 loglevel >= info，logging.debug 将不会记录消息。

这可能吗？

Answer 1

不，如果没有一些真正的技巧将当前函数转换为字符串并检查指令，您就不能创建这样的指令。不值得花时间检查。但是，您可以使用函数式装饰器来执行相同的功能，这有点棘手，但一旦您做到了，它就会非常强大。

我应该提到 es7 将有更容易实现的装饰器。它们仍然以相同的方式创建。它们是一个函数，即 returns 一个函数代替了原来的函数。但是他们有糖例如

sorry I couldn't stop so went a bit far. but now it's a pretty complete example.

@logLevel('warn')
function xyz(){
  // do some stuff
}

或

@logLevelInfo
function abc(){
  // do some stuff
}

// if this is false the logging will not occur
var __debug__ = true;
var __debug_levels__ = ['error', 'warn'];

// decorator to create a log level function. this is a function
// that takes the log type, that returns a function that takes the
// function you want to decorate with the logging functionality 
// that returns the decorated function that you call as xyz( ...arguments ).
function logLevel( type ) {
  return function logger(fn) {
    return function() {
      // save time if __debug__ is false
      if( __debug__ ){
        // run the decorated function and get the result
        // may as well wrap it in a try catch in case there are any errors
        try {
          var result = fn.apply(this, arguments);
        } catch( e ){
          console.error( e );
        }
        if( __debug_levels__.indexOf( type ) > -1 ){
          // log the result to the console or whatever functionality you require
          console[ type || 'log' ](result);
        }
        // return the result so you can do something with the result
        return result;
      }
      return fn.apply(this, arguments);
    }
  }
}

// this will return the first function that takes the function to decorate
var logLevelInfo = logLevel('warn');
var logLevelDebug = logLevel('error');


// here we are using the decorators to wrap the original function
var xyz = logLevelInfo(function xyz( arg ) {
  return arg + 'bar';
});

// same here but we are using the other decorator
var abc = logLevelDebug(function abc( arg ){
  return arg + 'baz';
});

// these functions have been decorated to perform the logging
// functionality on the returned result
xyz('foo'); //=> 'foobar'
abc('foo'); //=> 'foobaz'

<script src="http://codepen.io/synthet1c/pen/WrQapG.js"></script>

Answer 2

function Log(level)
{
    var levels = { 'debug': 10, 'info': 20};

    function write(lvl)
    {
        var handle = function(msg)
        {
            if (levels[lvl] <= levels[level]) 
                console.log(lvl + ': ' + msg);
        };

        return handle;
    }

    for (var i in levels)
    {
        this[i] = write(i);
    }
}

var log1 = new Log('info');
log1.info('hello'); // will result with an output
log1.debug('hello'); // still has an output output

var log2 = new Log('debug');
log2.info('hello'); // no output here

自定义 'use strict' 类指令

custom 'use strict' like directives

javascript

use-strict