How do I remove objects from a javascript associative array?

Suppose I have this code:

var myArray = new Object();
myArray["firstname"] = "Bob";
myArray["lastname"] = "Smith";
myArray["age"] = 25;

Now if I wanted to remove "lastname"?....is there some equivalent of
myArray["lastname"].remove()?

(I need the element gone because the number of elements is important and I want to keep things clean.)

Answers:

Answer

Use the "delete" keyword in Javascript.

delete myArray["lastname"];

EDIT:

In some JavaScript engine, the delete keyword might hurt performance as it will undo compile / JIT optimization.

http://www.html5rocks.com/en/tutorials/speed/v8/ http://www.smashingmagazine.com/2012/11/writing-fast-memory-efficient-javascript/

Answer

All objects in JavaScript are implemented as hashtables/associative arrays. So, the following are the equivalent:

alert(myObj["SomeProperty"]);
alert(myObj.SomeProperty);

And, as already indicated, you "remove" a property from an object via the delete keyword, which you can use in two ways:

delete myObj["SomeProperty"];
delete myObj.SomeProperty;

Hope the extra info helps...

Answer

None of the previous answers address the fact that Javascript does not have associative arrays to begin with - there is no array type as such, see typeof.

What Javascript has, are object instances with dynamic properties. When properties are confused with elements of an Array object instance then Bad Things™ are bound to happen:

Problem

var elements = new Array()

elements.push(document.getElementsByTagName("head")[0])
elements.push(document.getElementsByTagName("title")[0])
elements["prop"] = document.getElementsByTagName("body")[0]

console.log("number of elements: ", elements.length)   // returns 2
delete elements[1]
console.log("number of elements: ", elements.length)   // returns 2 (?!)

for (var i = 0; i < elements.length; i++)
{
   // uh-oh... throws a TypeError when i == 1
   elements[i].onmouseover = function () { window.alert("Over It.")}
   console.log("success at index: ", i)
}

Solution

To have a universal removal function that does not blow up on you, use:

Object.prototype.removeItem = function (key) {
   if (!this.hasOwnProperty(key))
      return
   if (isNaN(parseInt(key)) || !(this instanceof Array))
      delete this[key]
   else
      this.splice(key, 1)
};

//
// Code sample.
//
var elements = new Array()

elements.push(document.getElementsByTagName("head")[0])
elements.push(document.getElementsByTagName("title")[0])
elements["prop"] = document.getElementsByTagName("body")[0]

console.log(elements.length)                        // returns 2
elements.removeItem("prop")
elements.removeItem(0)
console.log(elements.hasOwnProperty("prop"))        // returns false as it should
console.log(elements.length)                        // returns 1 as it should
Answer

That only removes deletes the object but still keeps the array length same.

To remove you need to do something like:

array.splice(index, 1);
Answer

While the accepted answer is correct, it is missing the explanation why it works.

First of all, your code should reflect the fact that this is NOT an array:

var myObject = new Object();
myObject["firstname"] = "Bob";
myObject["lastname"] = "Smith";
myObject["age"] = 25;

Note that all objects (including Arrays) can be used this way. However, do not expect for standard JS array functions (pop, push,...) to work on objects!

As said in accepted answer, you can then use delete to remove the entries from objects:

delete myObject["lastname"]

You should decide which route you wish to take - either use objects (associative arrays / dictionaries) or use arrays (maps). Never mix the two of them.

Answer

Use method splice to completely remove item from an object array:

Object.prototype.removeItem = function (key, value) {
    if (value == undefined)
        return;

    for (var i in this) {
        if (this[i][key] == value) {
            this.splice(i, 1);
        }
    }
};

var collection = [
    { id: "5f299a5d-7793-47be-a827-bca227dbef95", title: "one" },
    { id: "87353080-8f49-46b9-9281-162a41ddb8df", title: "two" },
    { id: "a1af832c-9028-4690-9793-d623ecc75a95", title: "three" }
];

collection.removeItem("id", "87353080-8f49-46b9-9281-162a41ddb8df");
Answer

As other answers have noted, what you are using is not a Javascript array, but a Javascript object, which works almost like an associative array in other languages except that all keys are converted to strings. The new Map stores keys as their original type.

If you had an array and not an object, you could use the array's .filter function, to return a new array without the item you want removed:

var myArray = ['Bob', 'Smith', 25];
myArray = myArray.filter(function(item) {
    return item !== 'Smith';
});

If you have an older browser and jQuery, jQuery has a $.grep method that works similarly:

myArray = $.grep(myArray, function(item) {
    return item !== 'Smith';
});
Answer

There is an elegant way in Airbnb Style Guide to do this (ES7):

const myObject = {
  a: 1,
  b: 2,
  c: 3
};
const { a, ...noA } = myObject;
console.log(noA); // => { b: 2, c: 3 }

Copyright: https://codeburst.io/use-es2015-object-rest-operator-to-omit-properties-38a3ecffe90

Answer

You are using Object, you are not having an associative array to begin with. With an associative array, adding and removing items goes like this:

    Array.prototype.contains = function(obj) 
    {
        var i = this.length;
        while (i--) 
        {
            if (this[i] === obj) 
            {
                return true;
            }
        }
        return false;
    }


    Array.prototype.add = function(key, value) 
    {
        if(this.contains(key))
            this[key] = value;
        else
        {
            this.push(key);
            this[key] = value;
        }
    }


    Array.prototype.remove = function(key) 
    {
        for(var i = 0; i < this.length; ++i)
        {
            if(this[i] == key)
            {
                this.splice(i, 1);
                return;
            }
        }
    }



    // Read a page's GET URL variables and return them as an associative array.
    function getUrlVars()
    {
        var vars = [], hash;
        var hashes = window.location.href.slice(window.location.href.indexOf('?') + 1).split('&');

        for(var i = 0; i < hashes.length; i++)
        {
            hash = hashes[i].split('=');
            vars.push(hash[0]);
            vars[hash[0]] = hash[1];
        }

        return vars;
    }



    function ForwardAndHideVariables() {
        var dictParameters = getUrlVars();

        dictParameters.add("mno", "pqr");
        dictParameters.add("mno", "stfu");

        dictParameters.remove("mno");



        for(var i = 0; i < dictParameters.length; i++)
        {
            var key = dictParameters[i];
            var value = dictParameters[key];
            alert(key + "=" + value);
        }
        // And now forward with HTTP-POST
        aa_post_to_url("Default.aspx", dictParameters);
    }


    function aa_post_to_url(path, params, method) {
        method = method || "post";

        var form = document.createElement("form");

        //move the submit function to another variable
        //so that it doesn't get written over if a parameter name is 'submit'
        form._submit_function_ = form.submit;

        form.setAttribute("method", method);
        form.setAttribute("action", path);

        for(var i = 0; i < params.length; i++)
        {
            var key = params[i];

            var hiddenField = document.createElement("input");
            hiddenField.setAttribute("type", "hidden");
            hiddenField.setAttribute("name", key);
            hiddenField.setAttribute("value", params[key]);

            form.appendChild(hiddenField);
        }

        document.body.appendChild(form);
        form._submit_function_(); //call the renamed function
    }
Answer

You can remove an entry from your map by explicitly assigning it to 'undefined'. As in your case:

myArray["lastname"] = undefined;

Answer

If for whatever reason the delete key is not working (like it wasnt working for me )

You can splice it out and then filter the undefined values

// to cut out one element via arr.splice(indexToRemove, numberToRemove);
array.splice(key, 1)
array.filter(function(n){return n});

Dont try and chain them since splice returns removed elements;

Answer

We can use it as a function too. Angular throws some error if used as a prototype. Thanks @HarpyWar. It helped me solve a problem.

var removeItem = function (object, key, value) {
    if (value == undefined)
        return;

    for (var i in object) {
        if (object[i][key] == value) {
            object.splice(i, 1);
        }
    }
};

var collection = [
    { id: "5f299a5d-7793-47be-a827-bca227dbef95", title: "one" },
    { id: "87353080-8f49-46b9-9281-162a41ddb8df", title: "two" },
    { id: "a1af832c-9028-4690-9793-d623ecc75a95", title: "three" }
];

removeItem(collection, "id", "87353080-8f49-46b9-9281-162a41ddb8df");
Answer

Its very straight forward if you have underscore.js dependency in your project -

_.omit(myArray, "lastname")
Answer

By using the "delete" keyword, it will delete the array element from array in javascript.

For example,

Consider following statements.

var arrayElementToDelete = new Object();

arrayElementToDelete["id"]           = "XERTYB00G1"; 
arrayElementToDelete["first_name"]   = "Employee_one";
arrayElementToDelete["status"]       = "Active"; 

delete arrayElementToDelete["status"];

Last line of the code will remove the array element who's key is "status" from the array.

Answer

For "Arrays":

If you know the index:

array.splice(index, 1);

If you know the value:

function removeItem(array, value) {
    var index = array.indexOf(value);
    if (index > -1) {
        array.splice(index, 1);
    }
    return array;
}

The most upvoted answer for delete works well in case of objects but not for the real arrays. If I use delete it removes elements from loops but keeps the element as empty and length of array wont change. This may be a problem in some scenarios.

For example, if I do myArray.toString() on myArray after removal via delete it creates empty entry i.e. ,,

Answer

The only working method for me:

function removeItem (array, value) {
    var i = 0;
    while (i < array.length) {
        if(array[i] === value) {
            array.splice(i, 1);
        } else {
            ++i;
        }
    }
    return array;
}

usage:

var new = removeItem( ["apple","banana", "orange"],  "apple");
// ---> ["banana", "orange"]
Answer
var myArray = newmyArray = new Object(); 
myArray["firstname"] = "Bob";
myArray["lastname"] = "Smith";
myArray["age"] = 25;

var s = JSON.stringify(myArray);

s.replace(/"lastname[^,}]+,/g,'');
newmyArray = JSON.parse(p);

Without looping/iterates we get the same result

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