Check if object value exists within a Javascript array of objects and if not add a new object to array

Question

If I have the following array of objects       id  1  username   fred       id  2  username   bill       id  2  username   ted        Is there a way to loop through the array to check whether a particular username value already exists and if it does do nothing  but if it doesn t to add a new object to the array with said username  and new ID    Thanks

User · Accepted Answer

I ve assumed that ids are meant to be unique here  some is a great function for checking the existence of things in arrays    x000D   x000D  const arr      id  1  username   fred       id  2  username   bill       id  3  username   ted      x000D   x000D  function add arr  name    x000D    const   length     arr  x000D    const id   length   1  x000D    const found   arr some el   gt  el username     name   x000D    if   found  arr push   id  username  name     x000D    return arr  x000D    x000D   x000D  console log add arr   ted     x000D   x000D   x000D

User · Answer

There could be MULTIPLE POSSIBLE WAYS to check if an element in your case its Object  is present in an array or not   const arr         id  1  username   fred         id  2  username   bill         id  3  username   ted         let say you want to find an object with id   3  1  find  It searches for an element in an array and if it finds out then it returns that element else return undefined  It returns the value of the first element in the provided array that satisfies the provided testing function  reference const ObjIdToFind   5  const isObjectPresent   arr find  o    gt  o id     ObjIdToFind   if   isObjectPresent                  As find return object else undefined   arr push   id  arr length   1  username   Lorem ipsum         2  filter  It searches for elements in an array and filters out all element that matches the condition  It returns a new array with all elements and if none matches the condition then an empty array  reference const ObjIdToFind   5  const arrayWithFilterObjects  arr filter  o    gt  o id     ObjIdToFind   if   arrayWithFilterObjects length             As filter return new array   arr push   id  arr length   1  username   Lorem ipsum         3  some  The some   method tests whether at least one element is present in an array that passes the test implemented by the provided function  It returns a Boolean value  reference const ObjIdToFind   5  const isElementPresent   arr some  o    gt  o id     ObjIdToFind   if   isElementPresent                        As some return Boolean value   arr push   id  arr length   1  username   Lorem ipsum

User · Answer

const   checkIfElementExists       itemFromArray     gt    itemFromArray    sameKey        outsideObject    samekey        if  cartArray some checkIfElementExists             console log  already exists          else           alert  does not exists here

User · Answer

You could prototype your array to make it more modular  try something like this      Array prototype hasElement   function element            var i          for  i   0  i  lt  this length  i                  if  this i      element                    return i    Returns element position  so it exists                                  return -1    The element isn t in your array          And you can use it as    yourArray hasElement yourArrayElement

User · Answer

i did try the above steps for some reason it seams not to be working for me but this was my final solution to my own problem just maybe helpful to any one reading this    let pst   post likes some   like    gt       console log like user  req user id                                        if like user toString       req user id toString                                              return true                                              here post likes is an array of users who liked a  post

User · Answer

try this  first method using some    let arr      id  1  username   fred       id  2  username   bill       id  3  username   ted          let found   arr some ele   gt  ele username      bill        console log found    second method using includes  map     let arr      id  1  username   fred       id  2  username   bill       id  3  username   ted          let mapped   arr map ele   gt  ele username       let found   mapped includes  bill        console log found

User · Answer

It s rather trivial to check for existing username   var arr      id  1  username   fred          id  2  username   bill         id  3  username   ted       function userExists username      return arr some function el        return el username     username            console log userExists  fred        true console log userExists  bred        false   But it s not so obvious what to do when you have to add a new user to this array  The easiest way out - just pushing a new element with id equal to array length   1   function addUser username      if  userExists username         return false         arr push   id  arr length   1  username  username       return true     addUser  fred       false addUser  bred       true  user  bred  added   It will guarantee the IDs uniqueness  but will make this array look a bit strange if some elements will be taken off its end

User · Answer

Check it here    https   stackoverflow com a 53644664 1084987  You can create something like if condition afterwards  like   if  contains array  obj   add

User · Answer

Accepted answer can also be written in following way using arrow function on  some   function checkAndAdd name         var id   arr length   1       var found   arr some  el    gt               return el username     name                if   found    arr push   id  id  username  name

User · Answer

Here is an ES6 method chain using  map   and  includes     const arr       id  1  username   fred       id  2  username   bill       id  2  username   ted       const checkForUser    newUsername    gt          arr map user   gt            return user username          includes newUsername         if   checkForUser  fred          add fred      Map over existing users to create array of username strings  Check if that array of usernames includes the new username If it s not present  add the new user

User · Answer

I like Andy s answer  but the id isn t going to necessarily be unique  so here s what I came up with to create a unique ID also   Can be checked at jsfiddle too   Please note that arr length   1 may very well not guarantee a unique ID if anything had been removed previously   var array       id  1  username   fred       id  2  username   bill       id  3  username   ted       var usedname    bill   var newname    sam       don t add used name console log  before usedname      JSON stringify array    tryAdd usedname  array   console log  before newname      JSON stringify array    tryAdd newname  array   console log  after newname      JSON stringify array     function tryAdd name  array        var found   false      var i   0      var maxId   1      for  i in array               Check max id         if  maxId  lt   array i  id              maxId   array i  id   1              Don t need to add if we find it         if  array i  username     name              found   true             if   found          array   i      id  maxId  username  name

User · Answer

xorWith in Lodash can be used to achieve this  let objects       id  1  username   fred       id  2  username   bill       id  2  username   ted      let existingObject     id  1  username   fred     let newObject     id  1729  username   Ramanujan       xorWith objects   existingObject     isEqual     returns     id  2  username   bill       id  2  username   ted         xorWith objects   newObject     isEqual     returns     id  1  username   fred       id  2  username   bill       id  2  username   ted       id  1729  username   Ramanujan

User · Answer

I think that  this is the shortest way of addressing this problem  Here I have used ES6 arrow function with  filter to check the existence of newly adding username    var arr          id  1      username   fred           id  2      username   bill           id  3      username   ted       function add name        var id   arr length   1                      if  arr filter item  gt  item username    name  length    0               arr push   id  id  username  name                  add  ted    console log arr     Link to Fiddle

User · Answer

Let s assume we have an array of objects and you want to check if value of name is defined like this   let persons       name     test1     name    test2      if persons some person   gt  person name     test1              here your code in case person name is defined and available

User · Answer

This is what I did in addition to  sagar-gavhane s answer const newUser     id  4  name   Adam   const users      id  1  name   Fred      id  2  name   Ted      id  3  name  Bill     const userExists   users some user   gt  user name     newUser name   if userExists        return new Error  error  User exists      users push newUser

User · Answer

You can try this also  const addUser    name    gt        if  arr filter a   gt  a name    name  length  lt   0          arr push               id  arr length   1              name  name              addUser  Fred

User · Answer

function number present or not                 var arr     2 5 9 67 78 8 454 4 6 79 64 688             var found   6          var found two          for  i 0  i            if   found two    found                 console log  number present in the array              else               console log  number not present in the array

User · Answer

Native functions of array are sometimes 3X - 5X times slower than normal loops  Plus native functions wont work in all the browsers so there is a compatibility issues   My Code    lt script gt    var obj          function checkName name           declarations     var flag   0      var len   obj length         var i   0      var id   1          looping array     for  i  i  lt  len  i                 if name matches         if  name    obj i   username                  flag   1              break            else                  increment the id by 1             id   id   1                          if flag   1 then name exits else push in array     if  flag    0             new entry push in array               obj push   id  id   username   name                   function end    checkName  abc     lt  script gt    This way you can achieve result faster   Note  I have not checked if parameter passed is empty or not  if you want you can put a check on it or write a regular expression for particular validation

User · Answer

This small snippets works for me    const arrayOfObject      id  1  name   john      id  2  name   max      const checkUsername   obj   gt  obj name      max    console log arrayOfObject some checkUsername

[javascript] Check if object value exists within a Javascript array of objects and if not add a new object to array

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