Develop Reference

Alternatives to comparing object property using if...else

I hope I make my question clear.
I have a few objects which I have created with a property called address. For example, Obj1 has address 0x0000, Obj2 has address 0x0004 and so on.
There is a list of random input addresses which I need to process. Once the input address is one of the object address (if addr=0x0000||addr=0x0004....), then a function will be automatically loaded.
Currently, I am comparing it by a list of Object addresses, which I think is a waste of iteration. Is there any way, I can access it by index? For example, once I enter an input address of 0x0004, a function will be run directly.
edit : Thanks for all your answers :) I have a clearer idea now

You got 2 choices:
Use switch to define all functions:
switch (input){
case '0x0000': function(input){}; break;
case ...
}
Use a predefined map:
var functionMappings = {
'0x0000': function_1,
'0x0001': function_2,
};
if(functionMappings[input]) {
functionMappings[input](input);
}
I would prefer the second example, because it can be created dynamically in the runtime.
Update:
You can create your functionMappings dynamicaly like this:
var functionMappings = {// create first entries, or defualt functions
'0x0001': function_1,
'0x0002': function_2
};
if(condition_x) { // add new or overwrite existing functions
functionMappings[0x0005] = function_5;
}
Because this is an map, you can even overwrite default function definitions, if you need.

Iterate once and put all addresses as keys to an object:
var addresses = {};
for(var i=0;i<objList.length;i++){
addresses[objList[i].addr] = {};
addresses[objList[i].addr].fn = correspondingFunction
// you can even attach the corresponding object to it
// addresses[objList[i].addr].obj = addresses[objList[i].addr];
}
I use a loop for the example but you can do it any way that suits you
Then you have a list of your objects keyed by their address, and you can fetch them by it:
function getAddrFunction(addr){
if(addresses[addr] !== undefined){
return addresses[addr].fn;
}
return null;
}

Assign dynamic array to object

I want to pass following payload to the API
params[field1]: value1
params[field2]: value1
....
params[fieldN]: valueN
I have field and value coming from an object.
var params = {};
jQuery.each($scope.linkParams, function(a, b) {
params.params[a] = b; // returns undefined variable error
// I also tried other options but all result in one or another error
// Some doesn't result into an erro but doesn't get merged. See below merge requirement
});
I also wants to merge the above created object to another object with
jQuery.extend(extraParams, params);
How to achieve the rquired object?
Update
$scope.linkParams = {
field1: 'value1',
field2: 'value2',
....
};

You have two questions, so I'll address them one at a time.
(For a TL;DR, I emboldened the solution text. Hopefully the rest is worth the read, though.)
Object Serialization is Pretty Magical, but Not Quite That Magical
If I had a JS object that I instantiated like the following:
var cat = {
'meow': 'loud',
'type': 'Persian',
'sex': 'male'
}
then it is certainly true that you get attribute reference for free. That is, you can say something like cat.meow, and your runtime environment will make sense of that. However, JS will not automatically create properties of an object that you have referenced do not exist, unless you are referencing them to create them.
cat.health = 'meek' will work, but cat.ears[0] = 'pointy' will not.
var cat = {
'meow': 'loud',
'type': 'Persian',
'sex': 'male'
}
cat.health = 'meek'
alert(cat.health)
cat.ears[0] = 'pointy'
alert(cat.ears[0])
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
You'll notice that the first alert happens and contains the expected value, but the second alert never comes. This is because the code fails on the line with cat.ears[0] = 'pointy', and it stops execution at that point.
This may seem to contradict what I just said, but look closely at what's happening. When we attempt to initialize the first element of cat.ears, we must reference the cat.ears property, which does not exist.
JS implementations won't assume that you want to create items up the chain eternally, which is likely by design -- if it didn't throw errors and instead just created any properties or objects that needed to exist in order for your program to by syntactically sound, many pieces of software would silently break when they failed to include required libraries. If you forgot to include JQuery, it'd just create a $, a JQuery variable, and all of the properties of those objects you reference in your code. It'd be a proper mess to debug.
In short, that's what you're -- probably accidentally -- assuming will work here. params.params is analogous to cat.ears in the above example. You may have some reason for doing this, but assuming you don't, your code should function if you simply change params.params[a] to params[a].
JQuery.extend()
Assuming that extraParams is a valid array/object, the code you have written will work once params doesn't break your code anymore, however: do note that this will modify your extraParams object. If you want a new object to contain both params and extraParams, write something more like:
var args = $.extend({}, params, extraParams)
That will modify an empty object and add in the contents of params and extraParams. See the JQuery documentation for more information.

Some manipulations and I was able to achieve the required results.
I am posting the code for further reference:
var d = {};
jQuery.each($scope.linkParams, function(a,b) {
a = "params[" + a + "]";
d[a] = b;
});
jQuery.extend(extraParams, d);

Retrieving JS' Object value without knowing it's name

This is a fairly common question here in SO, and I've looked into quite a few of them before deciding to ask this question.
I have a function, hereby called CheckObjectConsistency which receives a single parameter, an object of the following syntax:
objEntry:
{
objCheck: anotherObject,
properties: [
{
//PropertyValue: (integer,string,double,whatever), //this won't work.
PropertyName: string,
ifDefined: function,
ifUndefined: function
}
,...
]
}
What this function does is... considering the given parameter is correctly designed, it gets the objCheck contained within it (var chk = objEntry.objCheck;), It then procedes to check if it contains the properties contained in this collection.
Like this
for(x=0;x<=properties.length;x++){
if(objCheck.hasOwnProperty(properties[x].PropertyName)){
properties[x].ifDefined();
}
else{
properties[x].ifUndefined();
}
What I want is... I want to bring it to yet another level of dynamicity: Given the propositions that IfDefined and IfUndefined are functions to be called, respectively, if the currently-pointed PropertyName exists, and otherwise, I want to call these functions while providing them, as parameters, the very objCheck.PropertyName's value, so that it can be treated before returning to the user.
I'll give a usage example:
I will feed this function an object I received from an external provider (say, a foreign JSON-returning-WebService) from which I know a few properties that may or may not be defined.
For example, this object can be either:
var userData1 = {
userID : 1
userName: "JoffreyBaratheon",
cargo: "King",
age: 12,
motherID : 2,
//fatherID: 5,--Not defined
Status: Alive
}
or
var userData2 = {
userID :
userName: "Gendry",
cargo: "Forger Apprentice",
//age: 35, -- Not Defined
//motherID: 4,-- Not Defined
fatherID: 3,
Status: Alive
}
My function will receive:
var objEntry=
{
objCheck: userData1,
properties: [
{
PropertyName: "age",
ifDefined: function(val){alert("He/she has an age defined, it's "+val+" !");},
ifUndefined: function(){alert("He/she does not have an age defined, so we're assuming 20.");},
},
{
PropertyName: "fatherID",
ifDefined: function(val){alert("He/she has a known father, his ID is "+val+" !");},
ifUndefined: function(){alert("Oh, phooey, we don't (blink!blink!) know who his father is!");},
}
]
}
CheckObjectConsistency(objEntry); // Will alert twice, saying that Joffrey's age is 12, and that his father is supposedly unknown.
ifDefined will only actually work if, instead of properties[x].ifDefined();, I somehow provide it with properties[x].ifDefined(PropertyValue);. And here, at last, lies my question.
Being inside the consistency-checking-function, I only know a given property's name if it's provided. Being inside it, I can't simply call it's value, since there is no such function as properties[x].ifUndefined(properties[x].GetValueFromProperty(properties[x].PropertyName)) ,... is there?
I'm sorry. Not being a native english speaker (I'm brazilian), I can't properly express my doubts in a short way, so I prefer to take my time writing a long text, in an (hopefully not wasted) attempt to make it clearer.
If, even so, my doubt is unclear, please let me know.

I think you're looking for the bracket notation here. It allows you to provide an arbitrary value as key to access the object. Also, you know its name. You have your properties object right?
objEntry.properties.forEach(function(property){
// Check if objCheck has a property with name given by PropertyName
if(!objEntry.objCheck.hasOwnProperty(property.PropertyName)){
// If it doesn't, call isUndefined
property.isUndefined();
} else {
// If it does, call isDefined and passing it the value
// Note the bracket notation, allowing us to provide an arbitrary key
// provided by a variable value to access objCheck which in this case is
// the value of PropertyName
property.isDefined(objEntry.objCheck[property.PropertyName]);
}
});
Oh yeah, forEach is a method of arrays which allows you to loop over them. You can still do the same with regular loops though.

Javascript/ Jquery Select object based on nested attribute

I'm trying to retrieve a nested object based on a nested nested id.
So my object is as follows
object = {
1: {
feature: {id:"1012"},
}
2: {
feature: {id:"3032"}
}
}
I have an id and I need to retrieve the corresponding object or to be more specific the object id. The object is a lot more complex but above shows the values that I need to retrieve.
I don't have much experience in JavaScript so am unsure how to achieve this. I've tried using Jquery's attribute selectors but have not been successful.
Any help would be appreciated.
Thanks.

if your "id" is mean like 1 or 2
do it like this:view it in JSFiddle
var obj = {
1: {
feature: {id:"1012"}
},
2: {
feature: {id:"3032"}
}
}
var getById = function(id){
return obj[id];
}
alert(getById(1).feature.id);
another way,if your id means like '1012','3032'
do it like this:view it in JSFiddle
my post about the Map in js

If I'm understanding the question correctly you are trying to use the id property of the object in each feature property to get the key (1, 2, etc) from object? So if you entered "1012" you would get back 1, if you entered "3032" you would get 2, etc?
If so this would do it:
var object = {
1: {
feature: {id:"1012"}
},
2: {
feature: {id:"3032"}
}
},
getIdByFeatureId = function (featureId) {
var id,
subObject;
// loop through each property of the object
for (id in object) {
// protect ourselves in case someone has tampered with Object.prototype
if (object.hasOwnProperty(id)) {
subObject = object[id];
if (subObject.feature.id === featureId) {
return id;
}
}
}
// none found? return null.
return null;
};
getIdByFeatureId("3032"); // returns 2
getIdByFeatureId("1012"); // returns 1
getIdByFeatureId("90210"); // returns null
You can play with the code in this fiddle.
Numbers stored as strings can be a pain, and often lead to confusion in how one need to call a function like this. One thing you might notice is I used the === strict equal operator. This only returns true if both values are exactly the same, including their type. It's good practice to use strict comparison operators unless you absolutely can't. It is also slightly faster since it doesn't have to coerce the values into a like type. But that means that you must pass a string into the function in order for it to match. You could use the non-strict equals == if you need it to be more flexible. If all of the feature ids are numeric (and none of them have leading zeros) and you have the ability to, I would change the feature ids to be actual numbers so you can keep it more intuitive by just passing in a number instead of a string representation of a number: getIdByFeatureId(3032); while keeping the strict comparison.

Javascript can't access property of an object

I have an object (returned from jQuery ajax) that looks like this:
data:{
materials:{
1:{
id:1,
name:"jacob"
}//1 (some integer)
}//materials
}//data
I'm trying to access name, but I can't get passed the object 1. I tried using makeArray() like this
var m = $.makeArray(data.materials);
var m0 = m.shift();
console.log(m);
console.log(m0);
$isArray(m) & $.isArray(m0) return true, but m and m0 both return:
1:{
id:1,
name:"jacob"
}//1 (some integer)
I expect that shift() to return the object that's inside of 1.
When I try to access m0.name it returns undefined, and when I try to access m[1] it returns undefined.
btw data.materials["1"].name works. the problem is 1 is variable (I don't know what it will be, so I wanted to use shift() which doesn't work on an object).
EDIT: So it seems that there is a limitation within makeArray(): since an object property is not supposed to be named with a number, that function does not convert the rest of the object and the output is some kind of object-array hybrid (on which you cannot use array functions like shift()), so the quick-n-dirty solution I came to was to loop thru it like this:
var m = data.materials,
id;
for ( key in m ) { id = key; }
console.log( m[id].name );
It's not all that clean, so if there's a better way, please let me know.
p.s. The 1:{} is there in the first place because the controller returns multiple "materials" under certain conditions (which will never be true when this js is used).

You should use data.materials["1"].name
http://jsfiddle.net/nq4RE/
Jacob, I see you updated your question.
To use a variable, you simply call data.materials[your_variable_here].name
http://jsfiddle.net/nq4RE/1/

Did you try: data.materials[1].name?
But in my opinion using number as property name is misleading.