Arrays in TypeScript should be typed, and all element values in it should conform to the type specified. There are two ways TypeScript allows the defining of the type to be done as shown here. The first is to use the array JavaScript type, followed by angle brackets, that contain the type's name. That's shown on line seven. This notation will be familiar, if you've done any C# or Java programming. The second is to use the type name, followed by empty square brackets, as on line 11. Again, this will be familiar to some of you. When defining the values in the array, they should all follow the array's type. As you would expect, the length is not fixed, and adding and removing elements, using push, pop, shift, and unshift, are allowed. We've shown these executed on lines 14 to 17, and all other array functions, available in JavaScript, can be used too. If you try to push a non-numeric value to our number array, say a string, you should at the very least get an error on compilation, and, if you're using an IDE with TypeScript set up in it, like VS Code that we're using, you should get error notation. You can see that we get this on line 20, where we try and push a string. And it tells us that type five is not assignable to parameter of type number. But what would happen if this was compiled? And we ignored the errors? Well yes, you'd get the valid JavaScript that allows this behavior, but if you're expecting an array of numbers to process, and you get a string in the middle, then your application is potentially going to fall over at some point. It's worth noting that destructuring TypeScript arrays works in the same way as it does in JavaScript. But what about situations where we want mixed types in an array? Let's have a look at tuples.

Lectures

Simple Types: An Introduction - Tuples - Any and Unknown - Null and Unidentified - Function Arguments and Return Types - Enums - Type Assertion