Passing arguments to a function within a JSON object

Question

When composing objects with functions, what's the proper way to pass parameters within the composition object?

For example:

// functions
const sayHi = () => {
    console.log('Hi!');
};

const greetPerson = (name) => {
    console.log(`Hello there, ${name}!`);
};

// "composition" objects, referring to the functions above
const hi = {
    'id': 1,
    'speak': sayHi
};

const greetWorld = {
    'id': 2,
    'speak': greetPerson('World')  // how do I go about passing the function a parameter here?
};

const greetMars = {
    'id': 3,
    'speak': greetPerson('Mars')
};

// register and run each
const salutations = [hi, greetWorld, greetMars];

for (let salutation of salutations) {
    salutation.speak();
}

The output when I run this is:

$ node sayHi.js
Hello there, World!
Hello there, Mars!
Hi!
/Users/rotarydial/sayHi.js:21
    salutation.speak();

TypeError: salutation.speak is not a function

How do I handle this properly so I can pass greetPerson() a parameter in the greet object?

Answer 1

I think this may be what you're looking for:

// functions
const sayHi = () => {
    console.log('Hi!');
};

const greetPerson = (name) => {
    console.log(`Hello there, ${name}!`);
};

// "composition" objects, referring to the functions above
const hi = {
    'id': 1,
    'speak': sayHi
};

const greet = {
    'id': 2,
    'speak': greetPerson // pass in a reference to the function for later use.
};

// register and run each
const salutations = [hi, greet];

for (let salutation of salutations) {
    salutation.speak("World!");
}

I suggest you read the MDN Working with Objects page, particularly the section Defining Methods

Here's an example from that page:

objectName.methodname = functionName;

var myObj = {
  myMethod: function(params) {
    // ...do something
  }

  // OR THIS WORKS TOO

  myOtherMethod(params) {
    // ...do something else
  }
};

Answer 2

In the code, greetPerson('World'), greetPerson('Mars') were getting executed at the time of object creation only.

const greetWorld = {
    'id': 2,
    'speak': greetPerson('World')
};

was getting evaluate to below after execution

const greetWorld = {
     'id': 2,
     'speak': undefined // as it was getting execute immediately, and function by default returns undefined if nothing explicitly returned from it.
};

Fix -

 // functions const sayHi = () => { console.log('Hi!'); }; const greetPerson = (name) => { console.log(`Hello there, ${name}!`); }; // "composition" objects, referring to the functions above const hi = { 'id': 1, 'speak': sayHi }; const greetWorld = { 'id': 2, 'speak': () => greetPerson('World') // how do I go about passing the function a parameter here? }; const greetMars = { 'id': 3, 'speak': () => greetPerson('Mars') }; // register and run each const salutations = [hi, greetWorld, greetMars]; for (let salutation of salutations) { salutation.speak(); }

Answer 3

我能够通过将带有参数的函数声明为匿名函数来使其工作，如下所示：

'speak': () => greetPerson('World')