calling apply for a function js code example

Example 1: apply() js

The apply() method accepts arguments in an array:

var arr = [6, 89, 3, 45];
var maximus = Math.max.apply(null, arr); // returns 89

Example 2: function calls

const obj = {
  foo: 1,
  get bar() {
    return 2;
  }
};

let copy = Object.assign({}, obj); 
console.log(copy); 
// { foo: 1, bar: 2 }
// The value of copy.bar is obj.bar's getter's return value.

// This is an assign function that copies full descriptors
function completeAssign(target, ...sources) {
  sources.forEach(source => {
    let descriptors = Object.keys(source).reduce((descriptors, key) => {
      descriptors[key] = Object.getOwnPropertyDescriptor(source, key);
      return descriptors;
    }, {});
    
    // By default, Object.assign copies enumerable Symbols, too
    Object.getOwnPropertySymbols(source).forEach(sym => {
      let descriptor = Object.getOwnPropertyDescriptor(source, sym);
      if (descriptor.enumerable) {
        descriptors[sym] = descriptor;
      }
    });
    Object.defineProperties(target, descriptors);
  });
  return target;
}

copy = completeAssign({}, obj);
console.log(copy);
// { foo:1, get bar() { return 2 } }