![]() TypeScript has helped make my JavaScript code so much more robust than it had ever been before, and the continued development of the language has been making everything even better all the time. You have no choice but to deal with optionality and undefined in JavaScript, but the great news is that there are a lot of tools available with which to deal with them. ![]() type Foo = Dealing with optionality isn’t optional. First, if you don’t tell TypeScript that a property is optional, it will expect it to be set. In strict mode, this means a couple of things. When you have a JavaScript object and you ask for a property that doesn’t exist, JavaScript will return undefined rather than throwing an error. I don’t think you can program JavaScript without having seen undefined is not a function at least once in your life - and once seems far too small a number. You must tell TypeScript if a property is optional. ![]() Here’s a full list: false 0 (zero) (empty string) null undefined NaN (Not A Number) Any other value in JavaScript is considered truthy. Both null and undefined are two of the six falsy values. TypeScript has tools to deal with all of these. In JavaScript there are only six falsy values.
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