The delete operator allows you to remove a property from an object.

The following examples all do the same thing.

// Example 1
var key = "Cow";
delete thisIsObject[key]; 

// Example 2
delete thisIsObject["Cow"];

// Example 3
delete thisIsObject.Cow;

let animals = {
  'Cow': 'Moo',
  'Cat': 'Meow',
  'Dog': 'Bark'
};

delete animals.Cow;
delete animals['Dog'];

console.log(animals);

If you're interested, read Understanding Delete for an in-depth explanation.

You should use immutable operations when using Redux. You should not change your state directly.

For that, you can use destructuring to exclude your todo from the todos, if your todos are in an object:

const { todos } = this.state;
const { [id]: _, ...newTodos } = todos;
this.setState({
    todos: newTodos
});

If the todos are in a list and since you cannot destructure an item by index from an array, use the slice method, which doesn't modify the array, but returns a modified copy:

const { todos } = this.state;
this.setState({
    todos: [...todos.slice(0, id), ...todos.slice(id + 1)];
});

Have you tried something like this?

function deleteByValue(val) {
    for(var f in fruits) {
        if(fruits[f] == val) {
            delete fruits[f];
        }
    }
}

And as per Rocket's comment, you might want to check hasOwnProperty to make sure you aren't deleting members of the object's prototype:

function deleteByValue(val) {
    for(var f in fruits) {
        if(fruits.hasOwnProperty(f) && fruits[f] == val) {
            delete fruits[f];
        }
    }
}

You can use something like this:

const data = {
  "/test2": {
    "path": "/test",
    "items": [{
      "path": "/test",
      "method": "GET",
    }, {
      "path": "/test",
      "method": "PUT",
    }]
  },
  "/test": {
    "path": "/test2",
    "items": [{
      "path": "/test2",
      "method": "GET",
    }]
  }
}

Object.keys(data).forEach(k => {
  data[k].items.forEach(item => {
    delete item['path']
  })
})

console.log(data)

jsfiddle

To remove a property from an object (mutating the object), you can do it by using the delete keyword, like this:

delete myObject.regex;
// or,
delete myObject['regex'];
// or,
var prop = "regex";
delete myObject[prop];

Demo

var myObject = {
  "ircEvent": "PRIVMSG",
  "method": "newURI",
  "regex": "^http://.*"
};
delete myObject.regex;

console.log(myObject);

For anyone interested in reading more about it, Stack Overflow user kangax has written an incredibly in-depth blog post about the delete statement on their blog, Understanding delete. It is highly recommended.

If you'd like a new object with all the keys of the original except some, you could use destructuring.

Demo

let myObject = {
  "ircEvent": "PRIVMSG",
  "method": "newURI",
  "regex": "^http://.*"
};

// assign the key regex to the variable _ indicating it will be unused
const { regex: _, ...newObj } = myObject;

console.log(newObj);   // has no 'regex' key
console.log(myObject); // remains unchanged

var test = {'red':'#FF0000', 'blue':'#0000FF'};
delete test.blue; // or use => delete test['blue'];
console.log(test);

this deletes test.blue