Develop Reference

Call a function defined inside another function on the same object in jQuery

var myfunction = function (obj1){
init = function(){
///object operation
func1();
}
func1 = function(){
some operation
}
}
In the above code there is a function called func1, defined inside myfunction operates on some object. Inside myfunction(), func1() is called to change the object, I want to call this object directly.

var func1 = ''
var myfunction = function(obj1) {
func1 = function(p, v) {
return p + ' - ' + v;
}
var init = function(data) {
return func1(obj1, data);
}
return init;
}
var d = myfunction('Hellow');
var result = d('world')
console.log('Inside call ', result)
console.log('Dirct call', func1('Hellow', 'World'))

influence Javascript function invokation

I want to invoke function X everytime any other function is invoked. I want to keep this as generic as possible.
having these two functions
function x(){ console.log("invoke BEFORE"); }
function someFunction(something){ console.log(something); }
When someFunction is invoked
someFunction("testoutput");
I want the console to output this:
>> invoke BEFORE
>> testoutput
I also want this behaviour to apply to any function of a certain object.
For example:
var myFunctions = {
first:function(){/* do something */},
second:function(){/* do something else*/}
}
myFunctions.before(function(){/do something before/});
Anyone know a solution?
EDIT:
I have come up with a solution like this:
Object.prototype.before = function(x){
for(var key in this){
if(typeof this[key] === "function")
this[key] = (function(x, f) {
var g = f;
return (function() {
x();
return g.apply(this, arguments);
});
}(x, this[key]));
}
}
var test = { func: function(){console.log("test")}};
test.before(function(){console.log("before")});
test();
results in:
>> before
>> test
YAAAYYY
how do you like this?

This is a bad idea that will make understanding and debugging your program much harder.
You can use what in Python is called "monkey-patching" to achieve this:
(function() {
{
var origSomeFunction = someFunction;
someFunction = (function() {
x();
return origSomeFunction.apply(this, arguments);
});
}();
This works because I changed the (global) name someFunction to refer to a new function that I defined. Within the closure of that function I keep a reference to the original function that you want to pass the call on to.

In my opinion, event binding is more flexible than function wrapping since you can remove x whenever you want. Here is a possible implementation:
// Observable
var Observable = {};
Observable.create = function (options) {
var observable = { events: {} };
var events = options.events || [];
var i, l = events.length;
for (i = 0; i < l; i++) {
observable.events[events[i]] = [];
}
return observable;
};
Observable.one = function (observable, event, handler) {
Observable.on(observable, event, function f () {
Observable.un(observable, event, f);
handler.apply(this, arguments);
});
};
Observable.on = function (observable, event, handler) {
observable.events[event].push(handler);
};
Observable.un = function (observable, event, handler) {
observable.events[event].splice(
observable.events[event].indexOf(handler), 1
);
};
Observable.emit = function (observable, event, params) {
var handlers = observable.events[event];
var i, l = handlers.length;
if (!params) params = {};
params.source = observable;
for (i = 0; i < l; i++) {
handlers[i].call(observable, params);
}
};
Observable.observeMethod = function (observable, name) {
var meth = observable[name];
var before = 'before' + name.toLowerCase();
var after = 'after' + name.toLowerCase();
observable.events[before] = [];
observable.events[after] = [];
observable[name] = function () {
var ret;
Observable.emit(observable, before);
ret = meth.apply(observable, arguments);
Observable.emit(observable, after, { value: ret });
return ret;
};
};
// init
var printer = init({
sayHello: function () {
this.print('Hello World.');
},
sayHi: function (e) {
this.print('Hi ' + e.pseudo + '.');
},
print: function (msg) {
print(msg);
}
});
var clock = init({
tid: null,
events: ['tick'],
stop: function () {
clearTimeout(this.tid);
},
start: function () {
var me = this;
var time = 0;
clearTimeout(this.tid);
(function tick () {
me.tid = setTimeout(tick, 1000);
me.emit('tick', { time: time++ });
})();
}
});
// demo: printer
printer.on('afterprint', printNewline);
printer.on('beforesayhello', printBullet);
printer.sayHello();
printer.sayHello();
printer.un('beforesayhello', printBullet);
printer.sayHello();
// demo: clock
clock.on('tick', function (e) {
if (e.time) printer.print('tick ' + e.time);
if (e.time === 3) this.stop();
});
clock.one('afterstop', clock.start);
clock.start();
// helpers
function init (obj) {
obj = initObservable(obj);
obj.one = function (event, handler) {
Observable.one(this, event, handler);
};
obj.on = function (event, handler) {
Observable.on(this, event, handler);
};
obj.un = function (event, handler) {
Observable.un(this, event, handler);
};
obj.emit = function (event, params) {
Observable.emit(this, event, params);
};
return obj;
}
function initObservable (obj) {
var k, observable;
observable = Observable.create({
events: obj.events
});
for (k in observable) {
obj[k] = observable[k];
}
for (k in obj) {
if (typeof obj[k] === 'function') {
Observable.observeMethod(obj, k);
}
}
return obj;
}
function printBullet () {
print('• ');
}
function printNewline () {
print('<br />');
}
function print (html) {
document.body.innerHTML += html;
}

Writing a function to set some but not necessarily all parameters in another function

I had a coding interview test that asked the following question which I was not able to fully solve. I'm wondering the best way to do this following my approach -- also sorry this is long.
You are given a function to read in like this (not necessarily 2 parameters):
function add(a, b) {
return a + b;
}
The objective is to create a function to initialize some of those variables and again call the function to perform the calculation like, function setParam(func, params). To use this you would do the following:
_add = setParam(add, {b:9})
_add(10) // should return 19
My solution was to parse the function to see how many parameters there are, then set them using the given parameters but since I barely know javascript I was never able to actually return a function with only some variables set and others still undefined.
(attempt at solution)
function setParam(func, params) {
// varray is an array of the the varriables from the function, func
// ie varray = [a,b] in this test
var varray = /function[^\(]*\(([^\)]*)\)/.exec(func.toString())[1].split(',');
//creates an array, paramset, that has the variables in func defined
//where possible
// ex paramset = [a,9] if only b was set
var paramsset = []
for (i = 0; i < varray.length; i++) {
if (typeof(params[varray[i]]) == "undefined"){
paramsset[i] = varray[i];
} else {
paramsset[i] = params[varray[i]];
}
}
//////
// need to modify existing function and return with added parameters
// where I'm stuck as this doesn't work.
newfunc = (function(){
var _func = func;
return function() {
return _func.apply(this, paramsset);
}
})();
newfunc()
}
I'm sure I'm not doing this the correct way, but any help would be appreciated.

I'm certainly not advocating to go towards that solution, but I still implemented something to follow your initial's API design for fun. The signatures weak map is necessary in order to preserve the initial function's signature so that we can call setParams again on partially applied functions.
var setParams = (function () {
var signatures = new WeakMap();
return function (fn, paramsToApply) {
var signature = signatureOf(fn), newFn;
validateParams(paramsToApply, signature.params);
newFn = function () {
var params = appliedParamsFrom(arguments, paramsToApply, signature.indexes);
return fn.apply(this, params);
};
signatures.set(newFn, signature);
return newFn;
};
function signatureOf(fn) {
return signatures.has(fn)?
signatures.get(fn) :
parseSignatureOf(fn);
}
function parseSignatureOf(fn) {
return String(fn)
.match(/function.*?\((.*?)\)/)[1]
.replace(/\s+/g, '')
.split(',')
.reduce(function (r, param, index) {
r.indexes[param] = index;
r.params.push(param);
return r;
}, { indexes: {}, params: [] });
}
function validateParams(paramsToApply, actualParams) {
Object.keys(paramsToApply).forEach(function (param) {
if (actualParams.indexOf(param) == -1) throw new Error("parameter '" + param + "' could not be found in the function's signature which is: 'function (" + actualParams + ")'");
});
}
function appliedParamsFrom(args, paramsToApply, paramsIndex) {
var appliedParams = [],
usedIndexes = [],
argsIndex = 0,
argsLen = args.length,
argSpotIndex = 0;
Object.keys(paramsToApply).forEach(function (param) {
var index = paramsIndex[param];
appliedParams[index] = paramsToApply[param];
usedIndexes.push(index);
});
while (argsIndex < argsLen) {
if (usedIndexes.indexOf(argSpotIndex) == -1) {
appliedParams[argSpotIndex] = args[argsIndex++];
}
++argSpotIndex;
}
return appliedParams;
}
})();
function add(a, b) { return a + b; }
var addTo9 = setParams(add, { b: 9 });
var add10To9 = setParams(addTo9, { a: 10 });
document.write(addTo9(10) + ', ' + add10To9());
Now, note that JavaScript comes with the Function.prototype.bind function which allows to perform in-order partial function application. The first parameter to bind has nothing to do with arguments, it's to bind the this value.
function add(a, b) { return a + b; }
var addTo9 = add.bind(null, 9);
document.write(addTo9(10));
And finally, an implementation with a placholder if you need one:
var partial = (function (undefined) {
var PLACEHOLDER = {};
function partial(fn, partialArgs) {
return function () {
return fn.apply(this, applyPartialArgs(arguments, partialArgs));
};
}
Object.defineProperty(partial, 'PLACEHOLDER', {
get: function () { return PLACEHOLDER; }
});
return partial;
function applyPartialArgs(args, partialArgs) {
var appliedArgs = partialArgs.map(function (arg) {
return arg === PLACEHOLDER? undefined : arg;
}),
partialArgsLen = partialArgs.length,
argsLen = args.length,
argsIndex = 0,
argSpotIndex = 0;
while (argsIndex < argsLen) {
if (
partialArgs[argSpotIndex] === PLACEHOLDER ||
argSpotIndex >= partialArgsLen
) {
appliedArgs[argSpotIndex] = args[argsIndex++];
}
++argSpotIndex;
}
return appliedArgs;
}
})();
function add(a, b, c, d) {
return a + b + c + d;
}
var _ = partial.PLACEHOLDER;
var addTo9 = partial(add, [_, 5, _, 4]);
document.write(addTo9(5, 5));

I'm guessing that they might have been testing for knowledge of partial application. (not currying)
Edit: Edited based upon your comments. This is Crockford's curry function straight from his book.
function add(a, b) {
return a + b;
}
if (!Function.prototype.partial) {
Function.prototype.partial = function() {
var slice = Array.prototype.slice,
args = new Array(arguments.length),
that = this;
for (var i = 0; i < args.length; i++) {
args[i] = arguments[i];
}
return function() {
return that.apply(null, args.concat(slice.apply(arguments)));
}
};
}
var example = add.partial(4);
console.log(example(10)); // output 14
console.log(example(20)); // output 24
var example = adder(4) assigns example to be function with a closure with a (in this case 4). When example is called like in the console.log, it will in effect be returning "the value of a when example was assigned, plus this new number."
Walkthrough of the partial() function:
Converts arguments to an array
returns a function gets passed the arguments given, which can be called later. It has a closure with the previously assigned arguments.

Why are my properties assigning incorrectly?

I created an ObservablePropertyList which is supposed to execute a callback when a property changes. The implementation is:
function ObservablePropertyList(nameCallbackCollection) {
var propertyList = {};
for (var index in nameCallbackCollection) {
var private_value = {};
propertyList["get_" + index] = function () { return private_value; }
propertyList["set_" + index] = function (value) {
// Set the value
private_value = value;
// Invoke the callback
nameCallbackCollection[index](value);
}
}
return propertyList;
}
And here's a quick test demonstration:
var boundProperties = BoundPropertyList({
TheTime: function (value) {
$('#thetime').text(value);
},
TheDate: function (value) {
$('#thedate').text(value);
}
});
var number = 0;
setInterval(function () {
boundProperties.set_TheTime(new Date());
boundProperties.set_TheDate(number++);
}, 500);
For some reason though, the properties are not being assigned correctly or something. That is, calling set_TheTime for some reason executes the callback for set_TheDate, almost as though it were binding everything to only the last item in the list. I can't for the life of me figure out what I'm doing wrong.

When using loops like that you need to wrap it in an enclosure
function ObservablePropertyList(nameCallbackCollection) {
var propertyList = {};
for (var index in nameCallbackCollection) {
(function(target){
var private_value = {};
propertyList["get_" + index] = function () { return private_value; }
propertyList["set_" + index] = function (value) {
// Set the value
private_value = value;
// Invoke the callback
target(value);
}
})(nameCallbackCollection[index]);
}
return propertyList;
}

You need to create a closure in order for each iteration of the for loop to have its own private_variable object. Otherwise, each iteration just overwrites the previous (since private_variable is hoisted to the top of its scope). I'd set it up like this:
var ObservablePropertyList = (function () {
"use strict";
var handleAccess = function (propList, key, callback) {
var privValue = {};
propList["get_" + key] = function () {
return privValue;
};
propList["set_" + key] = function (value) {
// Set the value
privValue = value;
// Invoke the callback
callback(value);
};
};
return function (coll) {
var propertyList = {}, index;
for (index in coll) {
handleAccess(propertyList, index, coll[index]);
}
return propertyList;
};
}());
var boundProperties = ObservablePropertyList({
TheTime: function (value) {
$('#thetime').text(value);
},
TheDate: function (value) {
$('#thedate').text(value);
}
}), number = 0;
setInterval(function () {
boundProperties.set_TheTime(new Date());
boundProperties.set_TheDate(number++);
}, 500);
DEMO: http://jsfiddle.net/PXHDT/

Calling Method represented by string

I am being passed a string similar to below.
"Users_Controller.login"
"Users_Controller" represents the object below.
And "login" a method within it.
var Users_Controller = ( function () {
return{
login : function(vo, callback)
{......}
}
})();
Given only the string as a pointer,is it possible call the method?

You can use this function:
function getPropertyFromString(str, start) {
str = str.split(".");
var prop = start || window;
for (var i = 0; i < str.length; i++) {
if(prop == undefined)
return prop;
else
prop = prop[str[i]];
}
return prop;
}
getPropertyFromString("Users_Controller.login");
However, this does not allow bracket syntax.

Something like this?
var Users_Controller = (function () {
return {
login: function (name) {
alert("hello " + name);
},
logout: function (name) { alert("goodbye "+name); }
}
})();
var methods = {};
for (method in Users_Controller) {
methods["Users_Controller." + method] = Users_Controller[method];
}
methods["Users_Controller.login"]('john');
methods["Users_Controller.logout"]('john');