Freezing objects for immutability
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Posted on In JavaScript, const doesn’t mean a value is constant and unchangeable. We cannot assigned different values to them, but we can still change (“mutate”) them.
To make an object immutable, we have to freeze it with Object.freeze().
// the word `const` makes it sound like this object can never be modified
const dog = { name: "Coop" }
// dog → { name: "Coop" }
// we can still change properties of an object defined with `const`
dog.name = "Cooper"
// dog → { name: "Cooper" }
// we can also add new properties to it
dog.age = 3
// dog → { name: "Cooper", age: 3 }
// the only thing we cannot do is assign an entirely different object
dog = { name: "Emil" } // TypeError (cannot assign to readonly property)
// to prevent ALL changes to an object, we have to freeze it
const cat = Object.freeze({ name: "Milly" })
// cat → { name: "Milly" }
// frozen objects can’t be changed (these steps throw errors in strict mode)
cat.name = "Lilly"
cat.age = 9
// cat → { name: "Milly" }// the word `const` makes it sound like this object can never be modified
const dog = { name: "Coop" }
// dog → { name: "Coop" }
// we can still change properties of an object defined with `const`
dog.name = "Cooper"
// dog → { name: "Cooper" }
// we can also add new properties to it
dog.age = 3
// dog → { name: "Cooper", age: 3 }
// the only thing we cannot do is assign an entirely different object
dog = { name: "Emil" } // TypeError (cannot assign to readonly property)
// to prevent ALL changes to an object, we have to freeze it
const cat = Object.freeze({ name: "Milly" })
// cat → { name: "Milly" }
// frozen objects can’t be changed (these steps throw errors in strict mode)
cat.name = "Lilly"
cat.age = 9
// cat → { name: "Milly" }// the word `const` makes it sound like this object can never be modified
const dog = { name: "Coop" }
// dog → { name: "Coop" }
// we can still change properties of an object defined with `const`
dog.name = "Cooper"
// dog → { name: "Cooper" }
// we can also add new properties to it
dog.age = 3
// dog → { name: "Cooper", age: 3 }
// the only thing we cannot do is assign an entirely different object
dog = { name: "Emil" } // TypeError (cannot assign to readonly property)
// to prevent ALL changes to an object, we have to freeze it
const cat = Object.freeze({ name: "Milly" })
// cat → { name: "Milly" }
// frozen objects can’t be changed (these steps throw errors in strict mode)
cat.name = "Lilly"
cat.age = 9
// cat → { name: "Milly" }// the word `const` makes it sound like this object can never be modified
const dog = { name: "Coop" }
// dog → { name: "Coop" }
// we can still change properties of an object defined with `const`
dog.name = "Cooper"
// dog → { name: "Cooper" }
// we can also add new properties to it
dog.age = 3
// dog → { name: "Cooper", age: 3 }
// the only thing we cannot do is assign an entirely different object
dog = { name: "Emil" } // TypeError (cannot assign to readonly property)
// to prevent ALL changes to an object, we have to freeze it
const cat = Object.freeze({ name: "Milly" })
// cat → { name: "Milly" }
// frozen objects can’t be changed (these steps throw errors in strict mode)
cat.name = "Lilly"
cat.age = 9
// cat → { name: "Milly" }