Boolean type in Typescript - simple explanation

The most basic datatype is the simple true/false value, which JavaScript and TypeScript call a boolean value. In Typescript, we can assign four values to it, and thise are true, 'false,undefinedandnull` (when not using strictNullChecks):

If we use strictNullChecks, the only values we cann asign are true and false.

When using variables that work with boolean, I like to name them something from which we can infer we are dealing with this type - like in this case, using the word is in isLoggedIn (it can be yes -> true or no -> false). You can name them however you want, this is just a personal preference and I've seen quite a few people doing it. Try to store something different inside them, and again we get an error.

This type is super useful when it comes to controlling the flow of a program using conditional statements (if this is true, do that, if this if false, do that). I don't use it much with pure Javascript but since I am working with React, it comes in handy when trying to render things based on different conditions. Or, in conjunction with interfaces, I can make sure that the props I'm trying to pass to a component are the correct type, in this case, boolean.

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