![]() How these types behave depends on whether you have the strictNullChecks option on. TypeScript has two corresponding types by the same names. JavaScript has two primitive values used to signal absent or uninitialized value: null and undefined. The as const suffix acts like const but for the type system, ensuring that all properties are assigned the literal type instead of a more general version like string or number. In this situation, you can use a type assertion to specify a more specific type: Sometimes you will have information about the type of a value that TypeScript can’t know about.įor example, if you’re using document.getElementById, TypeScript only knows that this will return some kind of HTMLElement, but you might know that your page will always have an HTMLCanvasElement with a given ID. If you would like a heuristic, use interface until you need to use features from type. ![]() Interface names will always appear in their original form in error messages, but only when they are used by name.įor the most part, you can choose based on personal preference, and TypeScript will tell you if it needs something to be the other kind of declaration. ![]()
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