`delete` Keyword

Examples

// Creates the property adminName on the global scope.
adminName = 'xyz';

// Creates the property empCount on the global scope.
// Since we are using var, this is marked as non-configurable.
var empCount = 43;

EmployeeDetails = {
  name: 'xyz',
  age: 5,
  designation: 'Developer'
};

// adminName is a property of the global scope.
// It can be deleted since it is created without var,
// and is therefore configurable.
delete adminName;       // returns true

// On the contrary, empCount is not configurable
// since var was used.
delete empCount;       // returns false

// delete can be used to remove properties from objects.
delete EmployeeDetails.name; // returns true

// Even when the property does not exist, delete returns "true".
delete EmployeeDetails.salary; // returns true

// delete does not affect built-in static properties.
delete Math.PI; // returns false

// EmployeeDetails is a property of the global scope.
// Since it was defined without "var", it is marked configurable.
delete EmployeeDetails;   // returns true

function f() {
  var z = 44;

  // delete doesn't affect local variable names
  delete z;     // returns false
}

delete and the prototype chain

In the following example, we delete an own property of an object while a property with the same name is available on the prototype chain:

function Foo() {
  this.bar = 10;
}

Foo.prototype.bar = 42;

const foo = new Foo();

// foo.bar is associated with the
// own property.
console.log(foo.bar); // 10

// Delete the own property within the
// foo object.
delete foo.bar; // returns true

// foo.bar is still available in the
// prototype chain.
console.log(foo.bar); // 42

// Delete the property on the prototype.
delete Foo.prototype.bar; // returns true

// The "bar" property can no longer be
// inherited from Foo since it has been
// deleted.
console.log(foo.bar); // undefined

Deleting array elements

When you delete an array element, the array length is not affected. This holds even if you delete the last element of the array.

When the delete operator removes an array element, that element is no longer in the array. In the following example, trees[3] is removed with delete.

const trees = ['redwood', 'bay', 'cedar', 'oak', 'maple'];
delete trees[3];
console.log(3 in trees); // false

If you want an array element to exist but have an undefined value, use the undefined value instead of the delete operator. In the following example, trees[3] is assigned the value undefined, but the array element still exists:

const trees = ['redwood', 'bay', 'cedar', 'oak', 'maple'];
trees[3] = undefined;
console.log(3 in trees); // true

If instead, you want to remove an array element by changing the contents of the array, use the splice() method. In the following example, trees[3] is removed from the array completely using splice():

const trees = ['redwood', 'bay', 'cedar', 'oak', 'maple'];
trees.splice(3, 1);
console.log(trees); // ["redwood", "bay", "cedar", "maple"]

delete Keyword

Examples

delete and the prototype chain

Deleting array elements

`delete` Keyword