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

Similar questions

Error: The argument provided is of type 'unknown', which cannot be assigned to a parameter of type 'string'. This issue arose when attempting to utilize JSON.parse in a TypeScript implementation

The ability to submit a conversation chat is currently

Retrieving a single item from an array of objects with the help of body parser

What is preventing me from installing socket.io?

Ensure the form is properly validated before initiating the submission process on 2checkout

Differences between RxJs Observable<string> and Observable<string[]>

Trouble confirming the password field with regular expressions in angular.js

Searching for li elements that contain text values - a guide

Update Material-ui to include an inclusive Datepicker widget

AngularJS is failing to recognize the onload event when loading a URL

Updating Kendo by modifying the Angular model

What is preventing me from navigating to other pages in my React application?

Best Practices for Variable Initialization in Stencil.js

I can't figure out why my SCSS isn't loading, even though I've added it to the webpack.mix.js file in my Laravel project that's set up with React.js

Create a dynamic onClick event script and integrate it into Google Optimize

What is the impact of Javascript variable scope in the context of "for...in..." loops?

The UTF-8 data sent by JQuery AJAX is not being correctly processed by my server, but only in Internet Explorer

Discovering Angular 2 Service Change Detection

Choosing a default selected value from a dropdown list with multiple editing options

Is it possible to load modal content using ajax bootstrap pagination without having to refresh the main page?