Typescript - Check if an object property already exists

Question

I am currently working on a ToDo App in Angular that adds "Todo's" as objects like so and also checks if the value is empty:

addTodo(newTodoLabel) {
    var newTodo = {
      label: newTodoLabel
    };



    if(newTodo.label == '') {  
      this.errorMessage = "Task description can't be empty";
   } else {

    this.todos.unshift(newTodo);
    this.errorMessage = ''; 
    this.infoMessage = "";
   }
 }

It will be added to this array:

   todos = [
    {
      label: 'Add more task attributes'
    }
  ];

And here is the HTML code as well:

<form #formCtrl="ngForm">

<div class="input-append">
<input class ="inputTask" maxlength="80" placeholder="Please enter a task description" type="text" class="form-control" #newTodo required />

<button class="buttonTask" (click)="addTodo(newTodo.value); newTodo.value=''" type="button" class="btn btn-primary form-control" >Add task</button>

Now my question is, how can I also check if the same property already exists in this array? (so that two tasks with the same name can't be added)

What do you mean by the same name? Two records in `todos` to be same? — Hassan Imam, Jan 26 '18 at 12:41
@HassanImam Yes, so if a user wants to put a value that already exists in todos — Jeremy, Jan 26 '18 at 12:47

score 1 · Accepted Answer · answered Jan 26 '18 at 12:59

Before adding a new todo, you can check if it already exists using array#some. If it exists, display error message, otherwise add it.

addTodo(newTodoLabel) {
  var newTodo = {
    label: newTodoLabel
  };

  if(newTodo.label == '') {  
    this.errorMessage = "Task description can't be empty";
 } else {
  //Check for duplicate todos
  var isSame = this.todos.some(function(o){
    return o.label.toLowerCase() === newTodoLabel.toLowerCase();
  });

  if(isSame) {
    this.errorMessage = 'Already conatins the same todo'
  } else {
     this.todos.unshift(newTodo);
     this.errorMessage = ''; 
     this.infoMessage = "";
  }
 }
}

score 1 · Answer 2 · edited Jun 01 '18 at 03:18

When you have to check object keys, simply check the object itself, and the object keys you need like :

if (obj && obj.label && obj.label !== '') { myFunction() {} }

In case you have an array you can check the index too obj[i].label for example. In case you want to check every key at the same time you can look on the obj keys using :

if(obj) {
    Object.keys(obj).map((key) => {
      if(obj[key]) { console.log("your object key exists") }
    })
}

Typescript - Check if an object property already exists

2 Answers2