Two issues there:

1. You're seeming to try to direct modify this.state.tasks. It's important not to do that, never directly modify this.state or any object on it. See Do Not Modify State Directly in the React documentation for state.




2. You're passing an object to setState that is derived from the current state. It's important never to do that, too. :-) Instead, pass setState a function and use the state object it passes you when calling that function. From State Updates May Be Asynchronous in the documentation:

   
   
   

   
   

   Because this.props and this.state may be updated asynchronously, you should not rely on their values for calculating the next state... [Instead]...use a second form of setState() that accepts a function rather than an object.

   
   

   
   
   

   (my emphasis)

I figure your remove on an array was intended to be hypothetical, but for the avoidance of doubt, arrays don't have a remove method. In this case, the best thing to do, since we need a new array, is to use filter to remove all entries that shouldn't still be there.

So:

deleteTask(taskToDelete) {

    this.setState(prevState => {

        const tasks = prevState.tasks.filter(task => task.name !== taskToDelete);

        return { tasks };

    });

}