new Typescript “satisfies” operator

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The difference is what you can do with favoriteColors after you define it.

With satisfies, the actual type of the assigned object literal is used as the type of favoriteColors, the information about what keys and values it contains is preserved (the type of the object literal is just checked against the type it’s supposed to satisfy).

// Ensure that we have exactly the keys from 'Colors'.
const favoriteColors = {
    "red": "yes",
    "green": false,
    "blue": "kinda",
} satisfies Record<Colors, unknown>;
favoriteColors.blue.toUpperCase() //ok it's a string
favoriteColors.green.toUpperCase() // error, it's a boolean

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Without satisfies, the type of accessing the property of favoriteColors will be unknown since the type of favoriteColors will be Record<Colors, unknown> as declared in the annotation. The information from the object literal is lost.

// Ensure that we have exactly the keys from 'Colors'.
const favoriteColors: Record<Colors, unknown> = {
    "red": "yes",
    "green": false,
    "blue": "kinda",
};

favoriteColors.blue.toUpperCase() // error, favoriteColors.blue is unknown
favoriteColors.green.toUpperCase() // error, favoriteColors.green is unknown

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