JS Bin // source https://jsbin.com/ruqezep

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JS Bin</title>
</head>
<body>
  <h3>Check your console to see the output, press F12 and go to the console tab.</h3>
  
  You can also <a href="https://jsbin.com/ruqezep/edit">view and edit the code</a> if you want.
<script id="jsbin-javascript">
// ES5 so you don't have to care about the browser
var wrapper = function(context, fnName, modifierFunction) {
  var originalFn = context[fnName];
  
  // a nice default function in case you just want to display
  // the arguments and not modify them yourself
  var modifierFn = modifierFunction || function(fn, args) {
    console.log(fnName + ' called with arguments: ' + args);
    
    return fn.apply(this, args);
  };
  
  context[fnName] = function() {
    var args = Array.prototype.slice.call(arguments);
    
    return modifierFn.call(this, originalFn, args);
  };
};

// --- EXAMPLES ---

// wrapping the native JSON.parse function
wrapper(JSON, 'parse');
JSON.parse(JSON.stringify({ foo: 'bar', baz: 2 }));
// prints =>
// parse called with arguments:  ["{"foo":"bar","baz":2}"]

// wrapping a logger function to add a prefix
var logMsg = function(message, details) {
  console.log(message, details);
};

wrapper(window, 'logMsg', function modifierFn(originalFn, args) {
  // modify the log message to prepend
  args[0] = 'MY CUSTOM PREFIX: ' + args[0];
  
  return originalFn.apply(this, args);
});

logMsg('hello from logMsg');
// prints =>
// MY CUSTOM PREFIX:  hello from logMsg
</script>

// --- EXAMPLES ---

// wrapping the native JSON.parse function
wrapper(JSON, 'parse');
JSON.parse(JSON.stringify({ foo: 'bar', baz: 2 }));
// prints =>
// parse called with arguments:  ["{"foo":"bar","baz":2}"]

// wrapping a logger function to add a prefix
var logMsg = function(message, details) {
  console.log(message, details);
};

wrapper(window, 'logMsg', function modifierFn(originalFn, args) {
  // modify the log message to prepend
  args[0] = 'MY CUSTOM PREFIX: ' + args[0];
  
  return originalFn.apply(this, args);
});

logMsg('hello from logMsg');
// prints =>
// MY CUSTOM PREFIX:  hello from logMsg</script></body>
</html>