Delete property from object javascript

delete operator

The delete operator removes a property from an object. If the property’s value is an object and there are no more references to the object, the object held by that property is eventually released automatically.

Try it

Syntax

delete object.property delete object[property] 

Note: The syntax allows a wider range of expressions following the delete operator, but only the above forms lead to meaningful behaviors.

Parameters

The name of an object, or an expression evaluating to an object.

Return value

true for all cases except when the property is an own non-configurable property, in which case false is returned in non-strict mode.

Exceptions

Thrown in strict mode if the property is an own non-configurable property.

Description

The delete operator has the same precedence as other unary operators like typeof . Therefore, it accepts any expression formed by higher-precedence operators. However, the following forms lead to early syntax errors in strict mode:

delete identifier; delete object.#privateProperty; 

Because classes are automatically in strict mode, and private properties can only be legally referenced in class bodies, this means private properties can never be deleted. While delete identifier may work if identifier refers to a configurable property of the global object, you should avoid this form and prefix it with globalThis instead.

While other expressions are accepted, they don’t lead to meaningful behaviors:

delete console.log(1); // Logs 1, returns true, but nothing deleted 

The delete operator removes a given property from an object. On successful deletion, it will return true , else false will be returned. Unlike what common belief suggests (perhaps due to other programming languages like delete in C++), the delete operator has nothing to do with directly freeing memory. Memory management is done indirectly via breaking references. See the memory management page for more details.

It is important to consider the following scenarios:

• If the property which you are trying to delete does not exist, delete will not have any effect and will return true .
• delete only has an effect on own properties. If a property with the same name exists on the object’s prototype chain, then after deletion, the object will use the property from the prototype chain.
• Non-configurable properties cannot be removed. This includes properties of built-in objects like Math , Array , Object and properties that are created as non-configurable with methods like Object.defineProperty() .
• Deleting variables, including function parameters, never works. delete variable will throw a SyntaxError in strict mode, and will have no effect in non-strict mode.
  • Any variable declared with var cannot be deleted from the global scope or from a function’s scope, because while they may be attached to the global object, they are not configurable.
  • Any variable declared with let or const cannot be deleted from the scope within which they were defined, because they are not attached to an object.

  Examples

  Using delete

  Note: The following example uses non-strict-mode only features, like implicitly creating global variables and deleting identifiers, which are forbidden in strict mode.

  // Creates the property empCount on the global scope. // Since we are using var, this is marked as non-configurable. var empCount = 43; // Creates the property EmployeeDetails on the global scope. // Since it was defined without "var", it is marked configurable. EmployeeDetails =  name: "xyz", age: 5, designation: "Developer", >; // 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 // EmployeeDetails is a property of the global scope. delete EmployeeDetails; // returns true // On the contrary, empCount is not configurable // since var was used. delete empCount; // returns false // delete also does not affect built-in static properties // that are non-configurable. delete Math.PI; // returns false 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 

  This creates a sparse array with an empty slot. 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"] 

  Deleting non-configurable properties

  When a property is marked as non-configurable, delete won’t have any effect, and will return false . In strict mode, this will raise a TypeError .

  const Employee = >; Object.defineProperty(Employee, "name",  configurable: false >); console.log(delete Employee.name); // returns false 

  var creates non-configurable properties that cannot be deleted with the delete operator:

  // Since "nameOther" is added using with the // var keyword, it is marked as non-configurable var nameOther = "XYZ"; // We can access this global property using: Object.getOwnPropertyDescriptor(globalThis, "nameOther"); // // value: "XYZ", // writable: true, // enumerable: true, // configurable: false // > delete globalThis.nameOther; // return false 

  In strict mode, this would raise an exception.

  Deleting global properties

  If a global property is configurable (for example, via direct property assignment), it can be deleted, and subsequent references to them as global variables will produce a ReferenceError .

  .globalVar = 1; console.log(globalVar); // 1 // In non-strict mode, you can use `delete globalVar` as well delete globalThis.globalVar; console.log(globalVar); // ReferenceError: globalVar is not defined 

  Specifications

  Browser compatibility

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  See also

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  This page was last modified on Jun 7, 2023 by MDN contributors.

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  Источник

  How to Remove a Property from a JavaScript Object

  

  There are two ways to remove a property from a JavaScript object. There’s the mutable way of doing it using the delete operator, and the immutable way of doing it using object restructuring.

  Let’s go through each of these methods in this tutorial.

  Remove a Property from a JS Object with the Delete Operator

  delete is a JavaScript instruction that allows us to remove a property from a JavaScript object. There are a couple of ways to use it:

  The operator deletes the corresponding property from the object.

  let blog = ; const propToBeDeleted = 'author'; delete blog[propToBeDeleted]; console.log(blog); //

  The delete operation modifies the original object. This means that it is a mutable operation.

  Remove a Property from a JS Object with Object Destructuring

  Using the object restructuring and rest syntax, we can destructure the object with the property to be removed and create a new copy of it.

  After the destructuring, a new copy of the object gets created and assigned to a new variable without the property that we chose to remove.

  let blog = ; const < author, . blogRest >= blog; console.log(blogRest) // ; console.log(blog); //

  If we want to do this dynamically, we can do this:

  const name = 'propertToBeRemoved'; const < [name]: removedProperty, . remainingObject >= object; 

  It is also possible to remove multiple properties using the same syntax.

  Wrapping Up

  And those are the two ways to remove a property from a JavaScript object. If you have any questions, feel free to reach out to me!

  Источник