Typescript class method, constrained to class properties

Question

Given the following class:

class MyOb {
  foo: string; 

  setFields(props) {
    Object.assign(this, props);
  }
}

Is it possible to constrain the props parameter of setFields to the properties of MyObj? So that:

new MyOb().setFields({ foo: 'bar' })  // compiles
new MyOb().setFields({ x: 'bar' })    // fails, property x is not a part of MyOb

SLaks · Accepted Answer · 2018-04-12 23:24:13Z

3

You're looking for keyof and mapped types:

setFields(props: { [TKey in keyof MyOb]?: MyOb[TKey] } ) {

Note the ?, since you want each property to be optional.

Demo

Docs

answered Apr 12, 2018 at 23:24

SLaks

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1 Comment

CRice Over a year ago

I'd note that this will only allow you to set the public properties and methods of the class, but not private or protected ones. That's fine (even preferable) in most cases but it's something to be aware of.

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