Prototypal Inheritance Exercise

Add a new functionality in Date object

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Let's add a new function named lastYear of the Date object, that will return the 1 year earlier than current year.

Date.prototype.lastYear = function () {
  return this.getFullYear() - 1;
};
new Date('1900-10-10').lastYear();

Here we use function keyword instead of arrow method to use dynamic-scope instead of lexical-scope.

When using function keyword, the this context is the new Date.

But with arrow method the this context is the arrow method itself, given below,

() => {
  return this.getFullYear() - 1;
};

Manipulate the map functionality of Array

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Array.prototype.map = function (args) {
  const newArray = [];
  this.forEach(val => newArray.push(`manipulated ${val}`));
  return newArray;
};

console.log([1, 2, 3].map());

This will give us output

[ 'manipulated 1', 'manipulated 2', 'manipulated 3' ]

Creating own bind method using the apply or call

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Function.prototype.bind = function (whoIsCallingMe) {
  const self = this;
  return function () {
    return self.apply(whoIsCallingMe, arguments);
  };
};