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mixin

a mixin is a object containing methods that can be used by other objects without a need to inherit from it.

mixin inheritance
Object.assign()
- ⛔️ Object.assign causing TypeError
💈範例：
- - pollyfill for

replit ⟩ mixin

const { log } = console;

// -------------- Object.assign --------------

const target = { a: 1, b: 2 };
const source = { b: 4

Previousclass A vs. class A extends Object NextmergeWithoutOverride()

Last updated 3 years ago

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const str  = 'abc';
const bool = true;
const num  = 10;
const sym  = Symbol('foo');

// • primitives wrapped
// • null and undefined (sources) ignored
const obj = Object.assign({}, str, null, bool, undefined, num, sym);

// only "string wrappers" have own enumerable properties.
console.log(obj);     // { "0": "a", "1": "b", "2": "c" }

const { log } = console;

// ----------------------------------------------
// ❌ assign object to "null" (Error)
// ⛔ TypeError: 
//    Cannot convert undefined or null to object
//
//    let o1 = Object.assign(null, {a: 1});
//                           ^^^^  <----
// ----------------------------------------------

// ✅ assign object to "number" (it's OK)
//    "number" is wrapped to object.
let o2 = Object.assign(3, {a: 1});

let n = 5;

// --------------------------------------------
// ⛔ TypeError:
//    Cannot create property 'b' on number '5'
//
//    n.b = 3;
//    ^  <----
// --------------------------------------------

[
    o2,                      // [Number: 3] { a: 1 }
    typeof o2,               // 'object'    (⭐ NOT 'number'❗)
    o2 instanceof Number,    // true        (⭐ still a `Number`❗)
    o2.a,                    // 1
    
    o2 ==  3,    // true
    o2 === 3,    // false        (⭐ NOT the same thing❗)
    3  === 3,    // true
    o2 + 4,      // 7
    
    n + n.b,     // NaN          ( 5 + undefined )
    typeof n,    // 'number'
    
].forEach(x => log(x));