Typescript for beginners: how to ignore code

Typescript is one of the best things that have happened in JavaScript world. It is a solid tool that checks for errors before they have happened. But sometimes we want to turn it off for some code.

There are several ways to ignore code in typescript:

Ignore code line with @ts-ignore rule:

this will ignore the code that is one line below

// @ts-ignore
const myAge : number = "25" // no typescript error
const isTrue : boolean = 4; // error

Usually this would throw an error about variable myAge not being type of number, but with @ts-ignore this error will be ignored.

Ignore code block with @ts-nocheck:

// @ts-nocheck
const myAge : number = "25" // no error
const isTrue : boolean = 4; // no error

🚨🚨@ts-nocheck will ignore the file, so if you want to ignore typescript checking on one function put it in separate file🚨🚨

This typescript rule should be used at the top of the file and it will ignore all code in the file.

**Typescript is meant to be helpful and allows us to write more robust, better structured code. Also it helps us to catch errors early, so use @ts-ignore and @ts-nocheck rules with caution.

Comments

[Emmanuel Mahuni]

What actually wanted to do is make the compiler ignore the line completely and not even compile it. The reason is it's changing the code in such a way that it becomes useless. So I wanted ts to actually ignore the line completely and move to the next. In other words copy the line as it is and paste it in the output code.
I want the following line to remain that way:

isAsyncFunction = (fn: Function) => fn instanceof Object.getPrototypeOf(async function(){}).constructor;

ts compiles this to:

isAsyncFunction = (fn) => fn instanceof Object.getPrototypeOf(function () {
    return __awaiter(this, void 0, void 0, function* () { });
}).constructor;

I want it to at least not change how the line is going to behave.

[Emmanuel Mahuni]

What I ended up doing was protect the code in an eval statement.

[Lars Rye Jeppesen]

In my opinion you should not teach beginners this. This will make it too easy to hide errors, every time they hit something they don't understand.

ts-ignore should be used very very reluctantly, not as a tool for beginners to ignore compilation errors.

[lborgman]

Right at this moment I am one of this beginners. And as usual when I try something new in IT I immediately stumble on a bug - in TypeScript this time.

//@ts-ignore was what I needed. Hiding this from beginners seems to me to be a very, very bad idea. I think you assume that beginners have not been programming before. That is just wrong.

[Chad Adams]

This is mostly used in situations where you are writing units tests. Say you want to test a function that takes a large complex object, but only operates on a smaller set of its data. you can pass in a smaller object missing the un-required keys, but that will throw a type error. This is a simple way around that.