Tips for setting default values for named parameters in JavaScript

Question

Tips for setting default values for named parameters in JavaScript

In my TypeScript method, I am using named parameters like this

public foo({x, y, z , m , n} : {x:string, y: number, z: number, m?:string, n?:number}) {
}

The parameters m and n will be provided from another object like

const defaults = { m : 'M', n :10, o:6 }

Now, I want to call the foo function like below and automatically add default parameters without explicitly passing them

  foo({x:'x', y: 5, z: 0})

My question is how can I apply the defaults within the body of foo, or somehow intercept the function before calling it and apply the defaults

public foo({x, y, z , m , n} = {x:string, y: number, z: number, m?:string, n?:number}) {
   // How can I apply defaults here?

}

Just for simplicity, I have reduced the number of parameters

I am aware of the following solutions already, but I'm looking for something with less boilerplate code

public foo({x, y, z , m , n} = {x:string, y: number, z: number, m?:string, n?:number}) {
   if (!m) {
     m = defaults.m;
   }
   if (!n) {
     n = defaults.n;
   }

}

or

foo({...defaults, x:'x', y: 5, z: 0 });

javascript typescript named-parameters

Answer 1

Answer №1

When merging objects, it is important to use destructuring along with the merge process. Default assignment may not function as expected in this scenario. Default assignment only comes into play when dealing with undefined objects being passed as values. To properly merge default values with passed values, utilize the de-structuring technique.

Be sure to review the comments within the code for further clarification.

interface Foo {
  x: string;
  y: number;
  z: number;
  m?: string;
  n?: number;
  o?: number;
}
const defaultValue = { m: "M", n: 10, o: 6 } as Foo;
class A {
  public foo(props: Foo) {
    const { x, y, z, m, n } = { ...defaultValue, ...props };
    console.log(x, y, z, m, n);
  }
  public foo2({ x, y, z, m = defaultValue.m, n = defaultValue.n }: Foo) {
    // although functional, this method can be verbose
    console.log(x, y, z, m, n);
  }
  public foo1({ x, y, z, m, n }: Foo = defaultValue) {
    // this method will only work if foo1 is called without any arguments
    console.log(x, y, z, m, n);
  }
  public print() {
    this.foo({ x: "x", y: 5, z: 0 }); // outputs: x 5 0 M 10
    this.foo1(); // outputs: undefined undefined undefined 'M' 10
    this.foo1({ x: "x", y: 5, z: 0 }); // outputs: x 5 0 undefined undefined
    this.foo2({ x: "x", y: 5, z: 0 }); // outputs: x 5 0 M 10
  }
}
const a = new A();
a.print();

The functions foo and foo2 are effective methods for merging objects. However, when working with numerous arguments, foo2 can become cumbersome. Consider using Object.assign() or spread syntax ({...}) for a more efficient way of merging values.

Answer 2

When merging objects, it is important to use destructuring along with the merge process. Default assignment may not function as expected in this scenario. Default assignment only comes into play when dealing with undefined objects being passed as values. To properly merge default values with passed values, utilize the de-structuring technique.

Be sure to review the comments within the code for further clarification.

interface Foo {
  x: string;
  y: number;
  z: number;
  m?: string;
  n?: number;
  o?: number;
}
const defaultValue = { m: "M", n: 10, o: 6 } as Foo;
class A {
  public foo(props: Foo) {
    const { x, y, z, m, n } = { ...defaultValue, ...props };
    console.log(x, y, z, m, n);
  }
  public foo2({ x, y, z, m = defaultValue.m, n = defaultValue.n }: Foo) {
    // although functional, this method can be verbose
    console.log(x, y, z, m, n);
  }
  public foo1({ x, y, z, m, n }: Foo = defaultValue) {
    // this method will only work if foo1 is called without any arguments
    console.log(x, y, z, m, n);
  }
  public print() {
    this.foo({ x: "x", y: 5, z: 0 }); // outputs: x 5 0 M 10
    this.foo1(); // outputs: undefined undefined undefined 'M' 10
    this.foo1({ x: "x", y: 5, z: 0 }); // outputs: x 5 0 undefined undefined
    this.foo2({ x: "x", y: 5, z: 0 }); // outputs: x 5 0 M 10
  }
}
const a = new A();
a.print();

The functions foo and foo2 are effective methods for merging objects. However, when working with numerous arguments, foo2 can become cumbersome. Consider using Object.assign() or spread syntax ({...}) for a more efficient way of merging values.

Answer 3

Answer №2

To simplify the parameter setup, you can include default values directly in the parameter declaration like this:

public foo({x, y, z , m = 'a' , n = 10} = {x:string, y: number, z: number, m?:string, n?:number}) {
}

If you provide a value when calling the method, it will replace the default value. This approach eliminates the need for an if statement to check for the presence of a value.

You can still invoke the method using the following syntax:

foo({...default, x:'x', y: 5, z: 0 });

Answer 4

To simplify the parameter setup, you can include default values directly in the parameter declaration like this:

public foo({x, y, z , m = 'a' , n = 10} = {x:string, y: number, z: number, m?:string, n?:number}) {
}

If you provide a value when calling the method, it will replace the default value. This approach eliminates the need for an if statement to check for the presence of a value.

You can still invoke the method using the following syntax:

foo({...default, x:'x', y: 5, z: 0 });

Answer 5

Answer №3

Is it possible to combine and destructure objects within a function?

type someType = {x:string, y: number, z: number, m?:string, n?:number};
const initialValues = { m : 'M', n :10, o:6 }

function foo(obj: someType) {
  const {x, y, z , m , n} = {
    ...initialValues,
    ...obj
  }

}

Answer 6

Is it possible to combine and destructure objects within a function?

type someType = {x:string, y: number, z: number, m?:string, n?:number};
const initialValues = { m : 'M', n :10, o:6 }

function foo(obj: someType) {
  const {x, y, z , m , n} = {
    ...initialValues,
    ...obj
  }

}

Tips for setting default values for named parameters in JavaScript

Answer №1

Answer №2

Answer №3

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