How do I wrap a function in Javascript?

Personally instead of polluting builtin objects I would go with a decorator technique:

var makeSafe = function(fn){  return function(){    try{      return fn.apply(this, arguments);    }catch(ex){      ErrorHandler.Exception(ex);    }  };};

You can use it like that:

function fnOriginal(a){  console.log(1/a);};var fn2 = makeSafe(fnOriginal);fn2(1);fn2(0);fn2("abracadabra!");var obj = {  method1: function(x){ /* do something */ },  method2: function(x){ /* do something */ }};obj.safeMethod1 = makeSafe(obj.method1);obj.method1(42);     // the original methodobj.safeMethod1(42); // the "safe" method// let's override a method completelyobj.method2 = makeSafe(obj.method2);

But if you do feel like modifying prototypes, you can write it like that:

Function.prototype.TryCatchWrap = function(){  var fn = this; // because we call it on the function itself  // let's copy the rest from makeSafe()  return function(){    try{      return fn.apply(this, arguments);    }catch(ex){      ErrorHandler.Exception(ex);    }  };};

Obvious improvement will be to parameterize makeSafe() so you can specify what function to call in the catch block.

2017 answer: just use ES6. Given the following demo function:

function doThing(){  console.log(...arguments)}

You can make your own wrapper function without needing external libraries:

function wrap(someFunction){  function wrappedFunction(){    var newArguments = [...arguments]    newArguments.push('SECRET EXTRA ARG ADDED BY WRAPPER!')    console.log(`You're about to run a function with these arguments: \n  ${newArguments}`)    return someFunction(...newArguments)  }  return wrappedFunction}

In use:

doThing('one', 'two', 'three')

Works as normal.

But using the new wrapped function:

const wrappedDoThing = wrap(doThing)wrappedDoThing('one', 'two', 'three')

Returns:

one two three SECRET EXTRA ARG ADDED BY WRAPPER!

2016 answer: use the wrap module:

In the example below I'm wrapping process.exit(), but this works happily with any other function (including browser JS too).

var wrap = require('lodash.wrap');var log = console.log.bind(console)var RESTART_FLUSH_DELAY = 3 * 1000process.exit = wrap(process.exit, function(originalFunction) {    log('Waiting', RESTART_FLUSH_DELAY, 'for buffers to flush before restarting')    setTimeout(originalFunction, RESTART_FLUSH_DELAY)});process.exit(1);

Object.extend(Function.prototype, {Object.extend in the Google Chrome Console gives me 'undefined'Well here's some working example:

    Boolean.prototype.XOR =//  ^- Note that it's a captial 'B' and so//      you'll work on the Class and not the >b<oolean object        function( bool2 ) {            var bool1 = this.valueOf();           //         'this' refers to the actual object - and not to 'XOR'           return (bool1 == true   &&   bool2 == false)               || (bool1 == false   &&   bool2 == true);        } alert ( "true.XOR( false ) => " true.XOR( false ) );

so instead ofObject.extend(Function.prototype, {...})Do it like:Function.prototype.extend = {}