➕delete

🚧 under construction -> configurable

• JS ⟩ value ⟩ object ⟩ property ⟩ access ⟩ delete

• JS ⟩ statement ⟩ expression ⟩ operator ⟩ unary ⟩ delete

(unary operator)

deletes configurable property / element.

delete <expr>
// ⭐️ return true if `expr` is not a "property access expression"

👉 table of operators

🗺️

deleting property

⭐️

delete

• can't delete normal variables. they are considered unqualified❗

• only deletes object's own/configurable properties, not inherited ones.

• expects its operand to be an lvalue, if it is not an lvalue, the operator takes no action and returns true.

deleting an array element leaves a “hole” in the array and does not change the array’s length❗ (sparse array)

🔰 global variable/function as global object property

• these properties cannot be deleted with delete❗

👉 global var / function is global object property❗️

🔴

• unqualified identifier for delete.

  • delete of an unqualified identifier in strict mode❗️

• can't delete variable/function❗️

👥

• delete <expr> returns true if <expr> is not a property access expression.

• accidental global variable in sloppy mode❗️ - can be deleted by delete.

• strict mode

• array elements can be deleted with the delete operator.

💈

• replit：delete in sloppy/strict mode

// 'use strict';    // ⭐ toggle sloppy/strict mode

const { log } = console;

// declarations
let x = 3.14;                            // variable
function f1() { log('f1'); }             // function declaration
let f2 = function() { log('f2'); }       // function expression
let fruits = ["Banana", "Orange"];       // array
let person = { name: 'John', age: 18 };  // object

// log
[
    //            mode:  //  sloppy                strict
    // -----------------------------------------------------------
    delete x,            // ❌ false               ⛔ SyntaxError
    x,                   // 3.14

    delete f1,           // ❌ false               ⛔ SyntaxError
    f1,                  // [Function: f1]

    delete f2,           // ❌ false               ⛔ SyntaxError
    f2,                  // [Function: f2]

    delete fruits[1],    // ✅ true                 ✅ true
    fruits,              // ['Banana', <empty>]     ['Banana', <empty>]

    delete person.age,   // ✅ true                 ✅ true
    person,              // { name: 'John' }        { name: 'John' }
    
].forEach(x => console.log(x));

// ⛔ SyntaxError: Delete of an unqualified identifier in strict mode.

📗

• JavaScript: The Definitive Guide ⟩

  • 4.13.4 The delete Operator

  • 6.4 Deleting Properties

• itHome ⟩ 你不可不知的 JavaScript 二三事 ⟩

  • #Day12：看 Strict Mode 如何施展「還我漂亮拳」(1)

📘

• delete operator

🗣

• How can I unset a JavaScript variable?