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1. Objects are Soft Glass
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When you hand someone an object, you hand them the same piece, not a copy. Reshape it, and everyone holding that piece sees the new shape — because there was only ever one piece of glass.
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let glass = { color: "amber" };
+let apprenticeHolds = glass;
+apprenticeHolds.color = "rose";
+// glass.color is now "rose" too —
+// same reference, same glass.
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+
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2. const Locks the Grip, Not the Glass
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const only prevents you from swapping which piece your hand holds. You can still reshape the glass in your grip — you just can't grab a different piece entirely.
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const glass = { temp: 500 };
+glass.temp = 900; // fine — same piece, reshaped
+glass = { temp: 20 }; // TypeError:
+// Assignment to constant variable.
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3. Mutate the Rack, or Cast a New One
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push(), splice(), and index assignment change the array in place — everyone with a reference sees it. Spreading with [...rack] pours the same pieces into a brand new rack, leaving the original untouched.
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const rack = [cup, vase];
+rack.push(bowl); // mutates rack directly
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+const displayRack = [...rack, bowl];
+// a NEW array — rack itself is untouched
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+
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4. Object.freeze() Cools It Forever
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Freezing is the kiln-cooling step. Once cooled, the glass is solid — any attempt to reshape it silently fails (or throws in strict mode). The piece doesn't bend anymore. It cracks instead.
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const heirloom = Object.freeze({ color: "gold" });
+heirloom.color = "grey";
+// strict mode → TypeError: Cannot assign to
+// read only property 'color' of object
+console.log(heirloom.color); // still "gold"
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