Created
          January 17, 2022 15:24 
        
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  | const metaProp = Symbol.for("meta"); | |
| function withMeta(m, x) { | |
| Object.defineProperty(x, metaProp, { | |
| value: m, | |
| writable: true, | |
| configurable: true, | |
| enumerable: false, | |
| }); | |
| return x; | |
| } | |
| function meta(x) { | |
| return x[metaProp]; | |
| } | |
| function alterMeta(x, f) { | |
| x[metaProp] = f(x[metaProp]); | |
| return x; | |
| } | |
| function resetMeta(x) { | |
| delete x[metaProp]; | |
| return x; | |
| } | |
| const a = { foo: "bar" }; | |
| const b = withMeta({ version: 1 }, a); | |
| console.log(a, b, a === b); | |
| console.log( | |
| JSON.stringify(a), | |
| JSON.stringify(b), | |
| JSON.stringify(a) === JSON.stringify(b) | |
| ); | |
| console.log(Object.entries(a), Object.entries(b)); | |
| console.log(meta(a), meta(b)); | |
| const c = alterMeta(a, ({ version }) => ({ version: version + 1 })); | |
| console.log(meta(a), a, meta(c), c); | |
| const d = resetMeta(a); | |
| console.log(meta(a), a, meta(d), d); | 
      
      
  Author
  
  
        
      
            honzabrecka
  
      
      
      commented 
        Jan 17, 2022 
      
    
  
  
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