JavaScript FAQ: Deleting an array element

Question: How do I delete an array element in JavaScript?

Answer: Two different ways to delete an element myArray[n] from myArray are:

• delete myArray[n] (faster, but leaves a gap at index n)
• myArray.splice(n,1) (slower, but does not leave a gap in the array)

  For example, to delete the myArray[5] element from myArray (leaving a gap), use thedelete statement: delete myArray[5]. You can use myArray.hasOwnProperty(n) to check if the element myArray[n] is present in myArray. Note that setting the array elementto null or to undefined is not equivalent to deleting the element, as shown in the example below:

  var myArray = new Array(0,10,20,30,40);  
  
  // myArray[5] does not exist yet
  document.write(myArray[5]);                // undefined
  document.write(typeof myArray[5]);         // undefined
  document.write(myArray.hasOwnProperty(5)); // false
  
  // create myArray[5] by assignment
  myArray[5] = 1;                            // 1
  document.write(typeof myArray[5]);         // number
  document.write(myArray.hasOwnProperty(5)); // true
  
  myArray[5] = null;                         // null
  document.write(typeof myArray[5]);         // object
  document.write(myArray.hasOwnProperty(5)); // true
  
  myArray[5] = undefined;                    // undefined
  document.write(typeof myArray[5]);         // undefined
  document.write(myArray.hasOwnProperty(5)); // true
  
  delete myArray[5];                            
  document.write(myArray[5]);                // undefined
  document.write(typeof myArray[5]);         // undefined
  document.write(myArray.hasOwnProperty(5)); // false
  

  Just like deleting an array element, you can also delete an object property. However, in JavaScript you cannot delete a variable declared with the var keyword at the time of first use.