Deleting array elements in JavaScript - delete vs splice

What is the difference between using the delete operator on the array element and using the Array.splice method?

For example:

 myArray = ['a', 'b', 'c', 'd']; delete myArray[1]; // or myArray.splice (1, 1); 

Why even have the splice method if I can delete array elements as I can with objects?

The answer

These are different things that have different purposes.

splice is table-specific and, when used for deletion, removes table entries and moves all previous entries to fill the gap. (It can also be used to insert entries, or both at the same time.) splice will change the length of the array (assuming it is not a non-op call: theArray.splice(x, 0) ) .

delete is not table-specific; it is designed to be used on objects: it deletes a property (key-value pair) of the object on which you use it. It only applies to arrays because standard arrays (for example, untyped) in JavaScript are not really arrays *, they are objects with special processing for some properties, such as those whose names are " indexes of arrays "defined as string names" ... whose numerical value is between +0 ≤ i < 2^32-1 ") and the length . When you use delete to delete an array entry, all it does is delete the entry; it does not move subsequent entries to fill the vacuum, so the array becomes "sparse" (some entries are missing). It has no effect on the length.

Some of the current answers to this question incorrectly indicate that using delete "sets the entry to undefined ". It's not correct. It removes the entry (property) entirely, leaving a void.

Let's use code to illustrate the differences:

 console.log("Using `splice`:"); var a = ["a", "b", "c", "d", "e"]; console.log(a.length); // 5 a.splice(0, 1); console.log(a.length); // 4 console.log(a[0]); // "b" 

 console.log("Using `delete`"); var a = ["a", "b", "c", "d", "e"]; console.log(a.length); // 5 delete a[0]; console.log(a.length); // still 5 console.log(a[0]); // undefined console.log("0" in a); // false console.log(a.hasOwnProperty(0)); // false 

 console.log("Setting to `undefined`"); var a = ["a", "b", "c", "d", "e"]; console.log(a.length); // 5 a[0] = undefined; console.log(a.length); // still 5 console.log(a[0]); // undefined console.log("0" in a); // true console.log(a.hasOwnProperty(0)); // true