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How to remove last key:value pair in JavaScript

I am very new to JavaScript and I am trying to figure out how to set a function to remove the last key:value pair to the right, much like array.pop for an array. This is an assignment I am working on. It seems confusing to me because, from my limited understanding of JS their is no specific order in a list of properties in an object. If anyone has any insight I would appreciate it. Here is the object:
var array = {length:0, size:big, smell:strange};
this is where I have started to go, but just having a hard time completing the function:
array.pop = function() {
//...
};
Ultimately I would like it to turn out like this:
array = {length:0, size:big};
Thanks in advance.

Objects do not have any defined order of properties so there is no "last" property. You have to remove a property by name, not position.
You can, of course, iterate over the properties and inspect them as you iterate and decide whether you want to delete any given property by looking at its name. Some javascript implementations will preserve the order that properties were added, but that is specifically not guaranteed by the ECMAScript specification so it cannot be relied upon.

This will work
const car = {
color: 'blue',
brand: 'Ford'
}
let keys = Object.keys(car)
delete car[keys[keys.length-1]]
console.log(car)

This answer is good for those situtations where the key is dynamically generated numbers like 0,1,2,3,4 etc
const myObject = {
0: 'somestring',
1: 42,
2: false
};
delete myObject[`${Object.keys(myObject).length-1}`]
console.log(myObject);
output:
Object { 0: "somestring", 1: 42 }
this one line logic may not good when key is a string. So, carefully use it.

The snippet below demonstrates that "objects have no order", and an [inefficient] workaround: use an array alongside of the object, to store the order that the properties were added to the object.
Click to add random properties, and note the order that they appear below.
In CodePen (or on my webserver) the properties seem to be stored sorted numerically (even though they're stored as strings).
However, in the snippet below they seem to be ordered randomly.
Neither are the order that the properties are added.
It should be noted:
Unlike what common belief suggests (perhaps due to other programming languages like delete in C++), the delete operator has nothing to do with directly freeing memory. Memory management is done indirectly via breaking references.
More info: delete operator and Memory Management.
var obj={}, // object to store properties (keys) and values
props=[]; // array to store property names
add.onclick=function(){
var prop=rnd(), val=rnd(); // get 2 random numbers
obj[ prop ] = val; // add property & value → object
props.push( prop ); // add property name → array
updateInfo(); // display object
}
del.onclick=function(){
var lastProp=props.pop(); // get/remove last property name in array
delete obj[ lastProp ]; // remove property
updateInfo(); //display object
}
function rnd(){return Math.floor(Math.random()*1E5);} // random 0-99999
function updateInfo(){ // show pretty object 😘
info.innerHTML=JSON.stringify(obj).replace(/[\{\}]+/g,"").replaceAll(',','<br>');
}
<button id='add'>add new property</button>
<button id='del'>delete last added</button>
<div id='info'></div>

javascript array indexing with large integers

I have a strange problem. I need a multidimensional javascript array that has numeric indexes e.g.:
MyArray = new Array();
$(".list-ui-wrapper").each(function(){
var unique = $(this).attr('id').replace(/[^\d.]/g,'');
MyArray ["'"+unique+"'"] = new Array();
});
The unique is a 8 digit integer. So if I dont wrap it inside the quotes, the ListUI_col_orders array will become extremly big, because if the unique = 85481726 then javascript will fill the array with 85481725 undefined elements before the the new empty array at the 85481726th index.
My problem is that later if i generate the unique again i cannot access the array anymore:
var unique = $(this).attr('id').replace(/[^\d.]/g,'');
console.log(MyArray [unique]); // undefined
console.log(MyArray ['"'+unique+'"']); // undefined
console.log(MyArray [unique.toString()]); // undefined
Any tips?

If you are going to use an array that's mostly sparse, then use a Hash table instead.
eg, set your variable as follows:
ListUI_col_Orders = {};
Then your indexing will be a key, so you don't have to worry about all the interstitial elements taking up space.

...because if the unique = 85481726 then javascript will fill the array with 85481725 undefined elements before the the new empty array at the 85481726th index.
No, it won't. JavaScript standard arrays are sparse. Setting an element at index 85481725 results in an array with one entry, and a length value of 85481726. That's all it does. More: A myth of arrays
The problem is that you're trying to retrieve the information with a different key than the key you used to store it. When storing, you're using a key with single quotes in it (actually in the key), on this line of code:
MyArray ["'"+unique+"'"] = new Array();
Say unique is 85481726. That line then is equivalent to this:
MyArray ["'85481726'"] = new Array();
Note that the key you're using (the text between the double quotes) has ' at the beginning and end. The actual property name has those quotes in it. Since it doesn't fit the definition of an array index, it doesn't affect length. It's a non-index object property. (How can you add a property to an array that isn't an array index? Arrays are not really arrays, see the link above.)
Later, you never use that key when trying to retrieve the value:
var unique = $(this).attr('id').replace(/[^\d.]/g,'');
console.log(MyArray [unique]); // undefined
console.log(MyArray ['"'+unique+'"']); // undefined
console.log(MyArray [unique.toString()]); // undefined
The keys you tried there were 85481726, "85481726" (with double quotes), and 85481726 again. Note that you never tried '85481726' (with single quotes), which is the key you used originally. Since you didn't use the same key, you didn't get the value.
Either use consistent quotes, or (much better) don't use quotes at all. Don't worry about the array length being a large number, JavaScript arrays are inherently sparse. Adding an entry with a large index does not create several thousand undefined entries in front of it.
All of that being said, unless you need the "array-ness" of arrays, you can just use an object instead. Arrays are useful if you use their features; if you're not using their array features, just use an object.
More about the sparseness of arrays: Consider this code:
var a = [];
a[9] = "testing";
console.log(a.length); // 10
Although the length property is 10, the array has only one entry in it, at index 9. This is not just sophistry, it's the actual, technical truth. You can tell using in or hasOwnProperty:
console.log(a.hasOwnProperty(3)); // false
console.log("3" in a); // false
When you try to retrieve an array element that doesn't exist, the result of that retrieval is undefined. But that doesn't mean there's an element there; there isn't. Just that trying to retrieve an element that doesn't exist returns undefined. You get the same thing if you try to retrieve any other property the object doesn't have:
var a = [];
a[9] = "testing";
console.log(a[0]); // undefined
console.log(a[200]); // undefined
console.log(a["foo"]); // undefined
Final note: All of this is true of the standard arrays created with [] or new Array(). In the next spec, JavaScript is gaining true arrays, created with constructors like Int32Array and such. Those are real arrays. (Many engines already have them.)

Get object property value

I have an object that contains an array of objects from which I need to get a value of their properties.
As an example this is what I need to get:
Stronghold.bins.models[0].attributes.entity.title
Which returns "Stronghold Title 1"
function grabItemName(){
var itemName=$(Stronghold.bins).each(function(){
return this.models[0].attributes.entity.title == title;
console.log(itemName);
})
};
(if there is a better way for me to ask this question please let me know)
I apologize if this was poorly asked!
The current issue is that it does not understand the array value '[0]' and cannot read it as it is undefined. What do I need to do to grab the 'title' value of all items in the array?

What do I need to do to grab the 'title' value of all items in the array?
That's what .map [docs] is for. It lets you map each value in an array to another value.
In the following I assume you want to iterate over each Stronghold.bins.models, because iterating over Stronghold.bins does not make sense with the provided information:
var titles = $.map(Stronghold.bins.models, function(obj) {
return obj.attributes.entity.title;
});
// `titles` is now an array containing `.attributes.entity.title;` of
// each object.
The current issue is that it does not understand the array value '[0]' and cannot read it as it is undefined.
Well, that won't happend anymore ;) In your example you where iterating over the properties of the Stronghold.bins object. One of these properties is models itself (!) and I doubt that any other property value has a models property.

Try using the other version of the each function:
$.each(Stronghold.bins, function () {
});
The version you are using is for looping through an element on the page, e.g $('body div p').each(function() {}), which isn't what you want in this instance: You want to loop over the values contained in Stronghold.bins.

Javascript use reserved keyword as key

Doing so
var x = new Array();
x['length']=5;
will make x an array of 5 undefined items, but I actually want to have the value '5' stored at key 'length'.
Is that possible?

In javascript arrays do not have keys. You are looking for objects:
var x = {}
x.length = 5;

I have to parse a file containing many words and store the number of occurences of each word
Use an object, and make the words the keys. You aren't storing sequential / ordered data, so you shouldn't use an array.
var word_count = {};
for (var i; i < words.length; i++) {
var word = words[i];
if (word_count[word]) {
word_count[word]++;
} else {
word_count[word] = 1;
}

If you want to do this you'd be better off creating an object rather than an array. This should give you what you want.
var x = {};
x['length'] = 5;

You can call methods on a javascript object using two different syntaxes. The familiar 'dot' syntax with parens to invoke the method, and the square bracket syntax. You can 'call' a method on a javascript object using the syntax myObj["methodname"](args). This is handy when you want to construct the method name dynamically using strings. Remember, objects in javascript are very much like a hash table (dictionary) where keys denote property and function names. If a key's value holds a function, it can be invoked (using parentheses).
In your example, Array has a method called 'length'. You are inadvertently calling its setter (which sets the length of the array to empty values, i.e., undefined).
Putting that all aside, you really do want a hash (associative array) in this case. An array is an offset indexed data structure.
A simple object literal like myObj = {} will suffice to give you hash semantics (again, objects in javascript are already like hashes) and you can then call myObj.whatever = "some value"

You could use objects instead of arrays to store your data. But if you need to use Arrays (you might need to use their functionality), You could cripple the words and store them as array keys.
Use some kind of simple rule to follow to bypass all the possible keywords. For example prefix all your array keys with a "_" character. This way you could always restore the original words from the keys, by simply removing their first character, and you are sure you are not referencing any specific property of the Array objects (like the length property).

how to get the value 'dynamically' from an associative array in javascript?

i am trying to get a value from a key stored on a string variable proyNombre, but whenever i call it via the common method "myAssociativeArray.MyKey", it gets the variable 'proyNombre' as the key, instead of getting its value and passing it as a key.
proyectos.each(function(index){
var proyNombre = this.value;
if(!(proyNombre in myArray)){ // whenever the variable is undefined, define it
myArray[proyNombre] = horas[index].value-0 + minutos[index].value/60;
}
else{
console.log(myArray.proyNombre); //This doesnt work, it tries to give me the value for the key 'proyNombre' instead of looking for the proyNombre variable
console.log(myArray.this.value); //doesnt work either
}
});

Try:
console.log(myArray[proyNombre]);
myArray is actually an object in javascript. You can access object properties with object.propertyName or, object['propertyName']. If your variable proyNombre contained the name of a property (which it does) you can use the second form, like I did above. object.proyNombre is invalid - proyNombre is a variable. You can't do for example:
var myObject = {};
myObject.test = 'test string';
var s = 'test';
console.log(myObject.s); // wrong!!
but you could then do:
console.log(myObject.test);
console.log(myObject['test']);
console.log(myObject[s]);

You need to use the same syntax you used to set the value:
console.log(myArray[proyNombre]);

Simply access the value with myArray[proyNombre].

You're doing it right in the assignment: myArray[proyNombre]. You can use the same method to retrieve the variable.
If you change:
console.log(myArray.proyNombre);
console.log(myArray.this.value);
to
console.log(myArray[proyNombre]);
console.log(myArray[this.value]);
You should get the same value (the value for the key represented by the variable proyNombre) logged twice.
It's true that Javascript doesn't have associative arrays but objects in Javascript can be treated like associative arrays when accessing their members.