Typescript check not done correctly when used in JS constructor

Question

I'm using TypeScript to detect typing problems in plain JavaScript. This is possible via a limited set of JSDoc tags.

However, there's one strange issue with it. When a member is created in the constructor, its type isn't set.

In the screenshot below, VS Code complains correctly about assigning a number to a string inside the update method, and directly on an instance. But it doesn't notice the incorrect assignment in the constructor.

This only seems to happen in the constructor, as creating a member in the update method does mark the typing issue.

Is there a way to force these type checks also in the constructor?

Code:

// @ts-check

function MyClass() {
    /** @type {string} */
    this.str = 0;
};

MyClass.prototype.update = function() {
    this.str = 0
    /** @type {number} */
    this.num = ""
}

let inst = new MyClass()
inst.str = 0
inst.num = ""

@member isn't supported for TypeScript. I did try it, but then it doesn't complain about anything. And the reason I used an image is because otherwise it won't show the squiggles. But I'll add the code too. — sanderd17
– sanderd17, Commented Nov 13, 2018 at 15:56

Matt McCutchen · Accepted Answer · 2018-11-13 16:22:46Z

2

Add /** @constructor */ above function MyClass to check it as a constructor. See the documentation.

answered Nov 13, 2018 at 16:22

Matt McCutchen

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1 Comment

sanderd17 Over a year ago

Thank you, completely missed that part.

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