➕dot notation (.)

`obj . prop` syntax.

JS ⟩ value ⟩ object ⟩ property ⟩ access ⟩ dot notation
JS ⟩ statement ⟩ expression ⟩ operator ⟩ left-hand side ⟩ property access ⟩ dot natation

(property access expression) (🌟 chaining rules | table of operators )

use obj . prop to evaluate object property's value.

obj . prop    // `prop` must be an "identifier".

🈯 synonyms： "chaining", "chaining operator", "dot notation"

replit：dot notation

// ⭐️ 1. prop: invalid identifier
// ------------------------------
undeclared.1 = 'bad';  // ⛔ SyntaxError: Unexpected number
//        ^^

// ⭐️ 2. obj: "undeclared"
// -------------------------------
undeclared.prop;       // ⛔ ReferenceError: 'undeclared' is not defined

// ⭐️ 3. obj: "nullish"
// -------------------------------
null.prop              // ⛔ TypeError: Cannot read properties of null

// ⭐️ 4. obj: not "nullish"
// -------------------------------
(18).prop;            // ❗ undefined (no such `prop`)
(18).toString(16);    // ❓ "12" (property value, could be any value)

// object
let obj = {};

// ┌───────────────────┐
// │ valid identifiers │
// └───────────────────┘

obj.$1 = 'joe';       // ✅ can begin with $, _
obj.var = 'OK';       // ✅ reserved word is allowed❗

⭐ the "prop" part must be an identifier❗

⭐ use instead if obj may be ❗

the of a always creates/sets a property in the original object, it never modifies objects in the .

Previousproperty access expression Nextdot notation vs. decimal point

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// ⭐️ 1. prop: invalid identifier // ------------------------------ undeclared.1 = 'bad'; // ⛔ SyntaxError: Unexpected number // ^^ // ⭐️ 2. obj: "undeclared" // ------------------------------- undeclared.prop; // ⛔ ReferenceError: 'undeclared' is not defined // ⭐️ 3. obj: "nullish" // ------------------------------- null.prop // ⛔ TypeError: Cannot read properties of null // ⭐️ 4. obj: not "nullish" // ------------------------------- (18).prop; // ❗ undefined (no such `prop`) (18).toString(16); // ❓ "12" (property value, could be any value) // object let obj = {}; // ┌───────────────────┐ // │ valid identifiers │ // └───────────────────┘ obj.$1 = 'joe'; // ✅ can begin with $, _ obj.var = 'OK'; // ✅ reserved word is allowed❗