const __checkIfElementExists__ = __itemFromArray__ => __itemFromArray__.*sameKey* === __outsideObject__.*samekey*;

    if (cartArray.some(checkIfElementExists)) {
        console.log('already exists');
    } else {
        alert('does not exists here')

我假设这里的id是唯一的。Find是一个很棒的数组方法，用于检查数组中是否存在东西:

Const arr = [{id: 1，用户名:'fred'}， {id: 2，用户名:'bill'}， {id: 3，用户名:'ted'}]; 函数add(arr, name) { Const {length} = arr; Const id =长度+ 1; Const found = arr。求(el => el。用户名=== name); 如果(!发现)arr。推送({id，用户名:name}); 返回arr; ｝ console.log(添加(arr“ted”)); console.log(添加(加勒比海盗,“黛西”));

我喜欢Andy的回答，但是id不一定是唯一的，所以这里是我想出的创建唯一id的方法。也可以在jsfiddle上查看。请注意arr。如果之前已经删除了任何内容，length + 1可能无法保证唯一的ID。

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 };
}

这是我在@sagar-gavhane的回答之外所做的

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)

假设我们有一个对象数组，你想检查value of name是否像这样定义，

let persons = [ {"name" : "test1"},{"name": "test2"}];

if(persons.some(person => person.name == 'test1')) {
    ... here your code in case person.name is defined and available
}

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 < arr.length; i++) {
    if (found == arr[i]) {
      found_two = arr[i];
      break;
    }
  }
  if (found_two == found) {
    console.log('number present in the array');
  } else {
    console.log('number not present in the array');
  }
}