What we talk about when we talk about the javascript object model (donutJS)

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what we talk about @vaidehĳoshi when we talk about the javascript object model

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(we’re hiring!)

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{}

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let cat = {};

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let cat = { sound: “meow” };

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cat.sound

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cat.sound cat[“sound”]

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property descriptors

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meta objects for all the properties on an object

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meta objects for all the properties on an object

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cat.sound

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Object.getOwnPropertyDescriptor( cat, “sound” ); cat.sound

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Object.getOwnPropertyDescriptor( cat, “sound” ); { value: "meow", writable: true, enumerable: true, configurable: true } cat.sound

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{ value: "meow", writable: true, enumerable: true, configurable: true } cat.sound

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{ value: "meow", writable: true, enumerable: true, configurable: true } cat.sound

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value writable cat.sound

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value writable cat.sound data property

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data property

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data property has a value, which might be editable

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data property

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data property object string number

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let cat = { sayHi: function() { return “Hi!”; } };

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let cat = { sayHi: function() { return “Hi!”; } }; cat.sayHi = function() { return “No, I will not say hi. I am a cat.”; };

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Object.getOwnPropertyDescriptor( cat, “sayHi” ); { value: ƒ(), writable: true, enumerable: true, configurable: true }

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cat.sound

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{ value: "meow", writable: true, enumerable: true, configurable: true } cat.sound

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enumerable configurable

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enumerable configurable

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enumerable configurable for…in

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enumerable configurable for…in Object.keys()

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enumerable configurable

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getters & setters

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let cat = { sound: “meow”, };

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let cat = { sound: “meow”, }; get loudSound() { return this.sound.toUppercase() + Math.random(); }

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let cat = { sound: “meow”, }; get loudSound() { return this.sound.toUppercase() + Math.random(); }

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Object.getOwnPropertyDescriptor( cat, “loudSound” );

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Object.getOwnPropertyDescriptor( cat, “loudSound” ); { get: ƒ(), set: undefined, enumerable: true, configurable: true }

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get set cat.loudSound

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get set accessor property cat.loudSound

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accessor property

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has a pair of getter + setter functions accessor property

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accessor property

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set ƒ() accessor property

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set ƒ() get ƒ() accessor property

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get loudSound() { return this.sound.toUppercase() + Math.random(); }

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cat.loudSound() > "MEOW0.2812205663401923" get loudSound() { return this.sound.toUppercase() + Math.random(); }

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cat.loudSound() > "MEOW0.2812205663401923" get loudSound() { return this.sound.toUppercase() + Math.random(); } cat.loudSound() > "MEOW0.41972556946839834"

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cat.loudSound() > "MEOW0.2812205663401923" get loudSound() { return this.sound.toUppercase() + Math.random(); } cat.loudSound() > "MEOW0.41972556946839834" cat.loudSound() > “MEOW0.5109470702014649"

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cat.loudSound > "MEOW0.2812205663401923" cat.loudSound > "MEOW0.41972556946839834" cat.loudSound > “MEOW0.5109470702014649"

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data property accessor property

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extensible

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new properties can be added to the object extensible

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enumerable configurable

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no removing or adding of properties, but continue to write

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no removing or adding of properties, but continue to write Object.seal()

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let cat = { sound: “meow” };

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let cat = { sound: “meow” }; Object.seal(cat);

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let cat = { sound: “meow” }; Object.seal(cat); { configurable: false, enumerable: true, value: “meow”, writable: true }

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no removing or adding of properties and no writing to properties, either!

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no removing or adding of properties and no writing to properties, either! Object.freeze()

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let cat = { sound: “meow” };

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let cat = { sound: “meow” }; Object.freeze(cat);

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let cat = { sound: “meow” }; Object.freeze(cat); { configurable: false, enumerable: true, value: “meow”, writable: false }

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Object.freeze(cat);

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Object.freeze(cat); A getter’s value isn’t going to be frozen

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Object.freeze(cat); A getter’s value isn’t going to be frozen Properties that have other objects as their value need to be frozen

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enumerable

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only an object’s own properties are enumerable*

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only an object’s own properties are enumerable* *its parent’s (prototype) properties will not be enumerable

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Object. getOwnPropertyDescriptors([]) { length: { value: 0, writable: true, enumerable: false, configurable: false }, __proto__: Object }

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Object. getOwnPropertyDescriptors([]) { length: { value: 0, writable: true, enumerable: false, configurable: false }, __proto__: Object } we don’t want these to show up in a loop!

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objects are complex!

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objects are complex! but also super cool

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objects are complex! but also super cool don’t be afraid to peek under the hood at how they work!