TypeScript is a typed superset of JavaScript that compiles to plain JavaScript.

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Learn some of the new features of TypeScript 3.7

The videos shows you how to use the null coalescing operator (??) instead of logical or (||) to set default values in TypeScript 3.7 to prevent expected bugs in your code.

Using the Null Coalescing operator with TypeScript 3.7

TypeScript 3.7 adds support for optional chaining. This lesson shows you how to use it in your code to handle properties that can be null or undefined.

Optional Chaining with TypeScript 3.7

TypeScript 3.7 Videos

https://app.egghead.io/api/v1/lessons/typescript-using-the-null-coalescing-operator-with-typescript-3-7/subtitles

Instructor: [00:00] I'm going to start by assigning undefined to the variable vowel. I'm then going to assign the variable "correct" the value from the variable vowel, only if vowel is not undefined and not null. Otherwise, I'll use the default value 05. As developers, we like shorthand syntax. Commonly, we'll simply check vowel "or" and then a default value.

[00:27] I'm going to assign that to the variable "incorrect." Finally, I'll lock both of these to the console. When I run my code, you'll see both correct and incorrect are 05. If I assign vowel the number zero, then compile and execute my code again, you'll notice that the correct answer is zero and incorrect is 05. The reason incorrect is showing the default value instead of the value provided is that zero, NaN, and empty strings are all considered falsy.

[01:09] Starting with TypeScript 3.7, you can use the null coalescence operator as a shorthand syntax for explicitly checking if the value is null or undefined. Now when I compile or run my code, both correct and incorrect show zero.

https://app.egghead.io/api/v1/lessons/typescript-using-the-null-coalescing-operator-with-typescript-3-7/transcript

https://app.egghead.io/api/v1/lessons/typescript-optional-chaining-with-typescript-3-7/subtitles

Instructor: [00:00] I'm going to start by defining two interfaces. Interface A will have an optional property B of type B. Interface B will have a property C of type String. I'll then assign an object to the variable A with B and C defined. Finally, I'll log the value of C to the console. When I compile and execute the code, you see the output "Hello, World!"

[00:38] The problem with this code is that an empty object is also a valid value for A. If I compile my code and run it, I get an error because B is undefined, so it cannot access the property C. Starting with version 3.7, TypeScript supports optional chaining. This allows me to place a question mark after the B, which tells TypeScript to check if B is null or undefined before it tries to access property C.

[01:06] If B is null or undefined, it will immediately terminate the chain and return the value undefined. When I compile and execute my code now, I see the value undefined.

https://app.egghead.io/api/v1/lessons/typescript-optional-chaining-with-typescript-3-7/transcript

TypeScript 3.7 Videos

Rich Buggy

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