I need to combine some functions (modify 1st function), but I can't do it this way (it works, but is bad for me):
var a = function(){alert('a');};
var b = function(){alert('b');};
var c = a;
a = function(){c(); b();};
a();
Then I try to do this:
var a = function(){alert('a');};
var b = function(){alert('b');};
var rx = /^[\s\S]*\(([\s\S]*)\)\s*{([\s\S]*)}$/;
concat = function(f1,f2)
{
var q = f1.toString().replace(rx,'$1|$2').split('|');
var w = f2.toString().replace(rx,'$1|$2').split('|');
return (q[0]!=='' && w[0]!=='')?
new Function(q[0]+','+w[0],q[1]+w[1]):
(q[0]!=='')?
new Function(q[0],q[1]+w[1]):
new Function(w[0],q[1]+w[1]);
};
a = concat(a,b);
alert(a);
It works, but may be exist an easier way?
function concat(a, b) {
return function() {
a.call(this, arguments);
b.call(this, arguments);
};
}
Eval is evil, and parsing code with regexes is more evil.
You can even add varargs support:
function concat() {
var funcs = arguments;
return function() {
for (var i = 0; i < funcs.length; i++)
funcs[i].call(this, arguments);
};
}
Related
I'm troubleshooting some 3rd party code on a client's website. The client was having issues with the code not working. I found that the issue was related to bound JS functions. Arguments that were passed to the bound function were undefined. I couldn't figure out why. Everything seems fine. However, I then found that the client has overridden the Bind function. Here is what they have:
Function.prototype.bind = function(scope) {
var _function = this;
return function() {
return _function.apply(scope, arguments);
};
};
So if I create a function
var sumFunction = function(a, b){
console.log("a: " + a);
console.log("b: " + b);
return a + b;
}
Then bind that function:
var boundFunction = sumFunction.bind(null, 10);
When I call that bound function I get the following:
console.log(boundFunction(20));
a: 20
b: undefined
NaN
I found a similar SO question that was using the same bind function. javascript custom scope binding function
It appears that it used to work? The SO question I linked seemed to work back in 2013, but now it doesn't form me.
Is this just outdated? JavaScript isn't my main strength, but my client will want to know why their function is causing the problem.
I found the overridden bind function to be odd. Especially the line return _function.apply(scope, arguments); It seems like passing the entire arguments object is incorrect. Shouldn't it only send the arguments in array position 1 and higher? I tried changing that to this to test:
Function.prototype.bind = function(scope) {
var _function = this;
var newArgs = Array.prototype.slice.call(arguments, 1)
return function() {
return _function.apply(scope, newArgs );
};
};
But now I just get the following:
console.log(boundFunction(20));
a: 10
b: undefined
NaN
When the function is bounded, there might be an array of arguments after the 1st, so use slice(1) to get them. When the function is called, get the all the arguments, and concat both args arrays.
Concat both arrays of arguments:
Function.prototype.bind = function(scope) {
var _function = this;
var args1 = Array.prototype.slice.call(arguments, 1);
return function() {
var args2 = Array.prototype.slice.call(arguments, 0);
return _function.apply(scope, args1.concat(args2));
};
};
var sumFunction = function(a, b){
console.log("a: " + a);
console.log("b: " + b);
return a + b;
}
var boundFunction = sumFunction.bind(null, 10);
console.log(boundFunction(20));
However, calling slice on arguments, might cause the V8 engine to skip optimisation on the function. A better way would be to just iterate the arguments manually, and add them to a single array:
Function.prototype.bind = function(scope) {
var args = [];
var _function = this;
for(var i = 1; i < arguments.length; i++) { args.push(arguments[i]); }
return function() {
var newArgs = args.slice(0);
for(var i = 0; i < arguments.length; i++) { newArgs.push(arguments[i]); }
return _function.apply(scope, newArgs);
};
};
var sumFunction = function(a, b){
console.log("a: " + a);
console.log("b: " + b);
return a + b;
}
var boundFunction = sumFunction.bind(null, 10);
console.log(boundFunction(20));
I am trying to write a function that takes functions as arguments (as many as it gets) and returns them. The function funcArg should return 'Called me'. I used Array.prototype.slice.call(arguments); to create an array but I don't know how to call die functions in that array. Any ideas? Thanks!!
var caller = function() {
return "Called ";
};
var adder = function() {
return " me";
};
var funcArgs = function() {
var myArray = Array.prototype.slice.call(arguments);
}
funcArgs(caller);
funcArgs(calleradder);
You can do this using reduce.
var funcArgs = function() {
var functions = Array.prototype.slice.call(arguments);
return functions.reduce(function(total, f) {
return total + f();
}, '');
};
The way this works if you start off with an array of functions. We then go through each function one at a time. We then call that function and append it to the result of the previous function. Breaking this down into simpler code would look like this:
var funcArgs = function() {
var functions = [caller, adder];
var result = '';
result += functions[0](); // caller();
result += functions[1](); // adder();
return result;
};
If you have an array of functions you can loop over them with forEach.
var caller = function() {
return "Called "
}
var adder = function() {
return " me"
}
var funcArgs = function() {
var myArray = Array.prototype.slice.call(arguments);
myArray.forEach(function (fn) {
console.log(fn())
})
}
funcArgs(caller, adder); // "Called me"
If you want to actually return the values, rather than just console.log them, you can use reduce to return the strings concatenated (or whatever else)
var funcArgs = function() {
var myArray = Array.prototype.slice.call(arguments);
return myArray.reduce(function (acc, fn) {
return acc + fn()
}, '')
}
I'm starting with unit testing. I need to create some fake data to run the tests. So let's say inside a stubbed method I'm passing an obj as an argument and I do things with obj.obj1.obj2.data inside the function. Is there a way to set this fake object? So, given:
obj.obj1.obj2.data
It creates:
obj = {
obj1: {
obj2: {
data: 'whatever'}}}
So it would be at the end something like:
var obj = creator('obj.obj1.obj2.data', 20);
Assuming the string is only a set of objects (no arrays) this should be fairly straightforward. Just split the input string on . and then use a while loop to do the nesting.
function creator(str,val){
var tree = str.split('.');
var ret = {};
var cur = ret;
while(tree.length){
var name = tree.shift();
cur[name] = tree.length ? {} : val;
cur = cur[name];
}
return ret;
}
document.querySelector("#out").innerHTML = JSON.stringify(creator('obj.obj1.obj2.data',20));
<div id="out"></div>
Just in case anyone else in interested, I created a simple npm module with the function below (https://github.com/r01010010/zappy) check it out:
var objFrom = function(str, last_value){
var objs = str.split('.');
var r = {};
var last = r;
for(i=0; i < objs.length; i++) {
if(i !== objs.length - 1){
last = last[objs[i]] = {};
}else{
last[objs[i]] = last_value;
}
}
return r;
}
var obj = objFrom('obj1.obj2.data', 20);
console.log(obj.obj1.obj2.data);
var object = {}; //lots of stuff in here
var func = object.dosome;
object.dosome = function(a,b) {
func(a,b);
//someth else here i need to add
}
This works but ugly.
So is there a way to supplement object.dosome method, without creating a new variable containing it's function?
Some sort of parent.dosome?
maybe create a class Object and define in its protoype the dosome() method.
var Object = new function() {}; //lots of stuff in here
Object.prototype.dosome = function(a,b) {
func(a,b);
}
//and then
var myObject = new Object();
I think you should read a little about JS OOP. ES6 adds some nice syntactic sugar that can help you achieve what you want in fewer lines of code. Read more here.
However, if you don't want to have problems with the prototype chains, here's a simpler way of achieving what you want:
function chain (baseFunc, func) {
return function () {
var args = [].slice.call(arguments, 0);
args.unshift(baseFunc);
return func.apply(this, args);
};
}
Usage:
var obj = {
doSome: function (a, b) { return a + b; }
};
obj.doSome(4, 5); // 9
obj.doSome = chain(obj.doSome, function (baseFunc, a, b) {
var result = baseFunc(a, b);
return result + 10;
});
obj.doSome(4, 5); // 19
You can go one step further and get rid of the assignment:
function extend (instance, method, func) {
instance[method] = chain(instance[method], func);
}
extend(obj, "doSome", function (baseFunc, a, b) {
var result = baseFunc(a, b);
return result + 2;
});
obj.doSome(4, 5); // 21
I have some Javascript code spread over multiples files, yet I want to facilitate minification with an IFFE. Some methods must remain public.
Wikipedia suggests the implementation of accessors:
var counter = (function(){
var i = 0;
return {
get: function(){
return i;
},
set: function( val ){
i = val;
},
increment: function() {
return ++i;
}
};
}());
Unfortunately, declaring these from return is not easy when such functions are declared in multiple files.
Is the following a proper solution? If not, what is?
var counter = (function(){
var i = 0;
// Import js file 1...
this.get = function(){ return i; };
// Import js file 2...
this.set = function( val ){ i = val; };
// Import js file 3...
this.increment = function() { return ++i; };
return this;
}());
P.S.: I want to be able to perform the following calls:
counter.get();
counter.set(33);
counter.increment();
It seems like the pattern that you are interested in is something like this:
//file 1
var xy = (function (that) {
that.prop1 = 1;
return that;
}(xy || {}));
//file2
var xy = (function (that) {
that.prop2 = 2;
return that;
}(xy || {}));
This will result in a single global object xy that has two properties:
xy = {
prop1: 1,
prop2: 2
};