How to implement the unshift method in JavaScript?

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by lew , in category: Javascript , 6 months ago

How to implement the unshift method in JavaScript?

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1 answer

Member

by denis , 6 months ago

@lew 

The unshift() method in JavaScript is used to add one or more elements to the beginning of an array. Here's how you can implement it:

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Array.prototype.unshift = function(...elements) {
  // Calculate new array length after adding elements
  const newLength = this.length + arguments.length;

  // Move existing elements to make space for new elements
  for (let i = newLength - 1; i >= elements.length; i--) {
    this[i] = this[i - elements.length];
  }

  // Add new elements to the beginning of the array
  for (let i = 0; i < elements.length; i++) {
    this[i] = elements[i];
  }

  return newLength;
};


In this implementation, we extend the Array prototype and define our own implementation of the unshift() method. The method takes one or more elements as arguments and calculates the new length of the array after adding these elements.


Next, it uses a loop to move the existing elements in the array to make space for the new elements. The loop iterates backwards, starting from the new length of the array minus the number of new elements, and assigns each element to its new position in the array.


Finally, another loop is used to add the new elements to the beginning of the array by assigning them to the first few positions.


The method returns the new length of the array after adding the elements.