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!
This question is related to
javascript
arrays
object
for-loop
foreach
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 => user.name === newUser.name);
if(userExists) {
return new Error({error:'User exists'})
}
users.push(newUser)
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");
}
}
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 < 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)
You can try this also
const addUser = (name) => {
if (arr.filter(a => a.name == name).length <= 0)
arr.push({
id: arr.length + 1,
name: name
})
}
addUser('Fred')
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 <= 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 };
}
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:
<script>
var obj = [];
function checkName(name) {
// declarations
var flag = 0;
var len = obj.length;
var i = 0;
var id = 1;
// looping array
for (i; i < 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');
</script>
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.
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' } ]
This small snippets works for me..
const arrayOfObject = [{ id: 1, name: 'john' }, {id: 2, name: 'max'}];
const checkUsername = obj => obj.name === 'max';
console.log(arrayOfObject.some(checkUsername))
Check it here :
https://stackoverflow.com/a/53644664/1084987
You can create something like if condition afterwards, like
if(!contains(array, obj)) add();
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=> item.username == name).length == 0){
arr.push({ id: id, username: name });
}
}
add('ted');
console.log(arr);
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 => person.name == 'test1')) {
... here your code in case person.name is defined and available
}
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) => {
arr.map(user => {
return user.username
}).includes(newUsername)
}
if (!checkForUser('fred')){
// add fred
}
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) => { //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.
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) => {
return el.username === name;
});
if (!found) { arr.push({ id: id, username: name }); }
}
const __checkIfElementExists__ = __itemFromArray__ => __itemFromArray__.*sameKey* === __outsideObject__.*samekey*;
if (cartArray.some(checkIfElementExists)) {
console.log('already exists');
} else {
alert('does not exists here')
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.
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 => 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 => ele.username);
let found = mapped.includes('bill');
console.log(found)
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) => 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) => 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) => o.id === ObjIdToFind);
if (!isElementPresent) { // As some return Boolean value
arr.push({ id: arr.length + 1, username: 'Lorem ipsum' });
}
Source: Stackoverflow.com