Function parameters destructuring in JavaScript

Destructuring has another very important application area - passing function parameters. The bottom line is this: if a function takes an array as a parameter, we can set directly in the function declaration how to destructure this array.

Let's look at an example. Suppose we have a function that takes an array with a year, month and day as a parameter:

javascriptfunc([2025, 12, 31]);

Let's specify directly in the function parameter which variables this array should be split into:

javascriptfunction func([year, month, day]) {
  console.log(year);  // shows 2025
  console.log(month); // shows 12
  console.log(day);   // shows 31
}

The above construction should be considered as a single function parameter. You can add more parameters if you want:

javascriptfunc('str1', [2025, 12, 31], 'str2');

function func(param1, [year, month, day], param2) {
  console.log(param1); // shows 'str1'
  
  console.log(year);   // shows 2025
  console.log(month);  // shows 12
  console.log(day);    // shows 31
  
  console.log(param2); // shows 'str2'
}

And in the following example, arrays are passed as the first and second parameters to the function, and we destructure both of them:

javascriptfunc([2025, 12, 31], [2026, 11, 30]);

function func([year1, month1, day1], [year2, month2, day2]) {
  console.log(year1);  // shows 2025
  console.log(month1); // shows 12
  console.log(day1);   // shows 31
  
  console.log(year2);  // shows 2026
  console.log(month2); // shows 11
  console.log(day2);   // shows 30
}

javascriptfunction func(employee) {
  let name       = employee[0];
  let surname    = employee[1];
  let department = employee[2];
  let position   = employee[3];
  let salary     = employee[4];
}

func( ['John', 'Smit', 'development', 'programmer', 2000] );

javascriptfunction func(employee) {
  let name     = employee[0];
  let surname  = employee[1];
  let info     = employee[2];
}

func( ['John', 'Smit', 'development', 'programmer', 2000] );

javascriptfunction func(employee) {
  let name       = employee[0];
  let surname    = employee[1];
  let department = employee[2];
  
  let position;
  if (arr[3] !== undefined) {
    position = arr[3];
  } else {
    position = 'junior';
  }
}

func( ['John', 'Smit', 'development'] );

javascriptfunction func(department, employee, hired) {
  let name     = employee[0];
  let surname  = employee[1];
  
  let year  = hired[0];
  let month = hired[1];
  let day   = hired[2];
}

func( 'development', ['John', 'Smit'], [2018, 12, 31] );