prefer-class-properties.md

Prefer class properties to assignment of literals in constructors. (prefer-class-properties)

Class properties allow you to set initial values for instance properties, instead of setting these in the constructor of a class.

Rule Details

This rule takes one argument. If it is 'always' (default) then it warns when it finds an assignment to this in a class constructor that could instead be a class property. If set to 'never', it will warn when any class properties are found.

The following assignments are all considered warnings when using the default or explicitly setting the argument to 'always':

class Foo {
  constructor() {
    this.bar = 'bar';
    this.baz = 123;
    this.qux = {
      foo: 'bar',
      baz: [1, 2, 3];
    };
  }
}

The following assignments are not warnings when using the default or explicitly setting the argument to 'always':

class Foo {
  constructor(baz) {
    this.baz = baz;
    this.qux = this.initialize();
  }
}

The following are considered warnings when setting the argument to 'never':

class Foo {
  baz = 123;
  qux = something();
}

When Not To Use It

If you do not care how literal instance members are assigned, you can safely disable this rule.

Further Reading

• Class properties proposal