How Can I Simulate Named Parameters in JavaScript Function Calls?

Simulating Named Parameters in JavaScript Function Calls

In programming languages like C#, named parameters allow for clear and concise function calls by specifying parameter names alongside their values. JavaScript, however, does not inherently provide this feature. However, there are ways to achieve a similar effect.

ES2015 and Later: Parameter Destructuring

With the introduction of ES2015, parameter destructuring offers a built-in mechanism to simulate named parameters. Using this feature, a function can accept an object as an argument and extract specific properties as named parameters:

function myFunction({ param1, param2 } = {}) {
  // ...function body...
}

Callers can then pass an object with the desired parameter values:

myFunction({ param1: 70, param2: 175 });

ES5: Function.prototype.toString and Object Association

In ES5, a hackish method involves using Function.prototype.toString() to parse the function signature and identify parameter names. This allows us to associate properties of an object with the corresponding parameters:

var func = parameterfy(function(a, b, c) {
  console.log('a is ' + a, ' | b is ' + b, ' | c is ' + c);     
});

func(1, 2, 3); // a is 1  | b is 2  | c is 3
func(1, {b:2, c:3}); // a is 1  | b is 2  | c is 3

However, this approach has drawbacks:

• If the last argument is an object, it is treated as a "named argument object."
• The function will always receive all defined arguments, with undefined values as placeholders.

Additional Considerations

As an alternative to creating function wrappers, you can also have functions that accept a function and additional arguments, or extend Function.prototype to support executing functions with named parameters.

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