使用删除运算符

Question

I'm reading the delete unary operator talked about near bottom of page here ( https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Expressions_and_Operators#Unary )

It says deleting an item from an array will make the item undefined . However, as the code below shows, we cannot loop over this undefined item like we can do with a fresh array with the explicit value of undefined as one of its items.

Is this just a quirk or is there more to read into here? It doesn't seem meaningful to describe the deleted item as undefined when it's not treated like undefined .

 let a = [1, 2, 3]; console.log("untampered-with array:", a); delete a[0]; console.log("array after first item deleted:", a); a.forEach(element => { console.log("looping over each item and printing it:", element); }); b = [undefined, 1, 2]; b.forEach(element => { console.log("looping over each item of array with undefined explicitly declared:", element); });

It might also be worth mentioning that in Visual Studio Code, when we print out a after the first item is deleted, it does not show the first item as undefined (like it does on the Stack Overflow code simulator). It shows this:

Answer 1

You can use splice method to remove array items instead of using delete.

Answer 2

You can either use splice

let b = a.splice(0, 1)

https://developer.mozilla.org/fr/docs/Web/JavaScript/Reference/Objets_globaux/Array/splice

or filter

let b = a.filter((item, i) => { return i !== 0 })

https://developer.mozilla.org/fr/docs/Web/JavaScript/Reference/Objets_globaux/Array/filter

In both case, b is a new array without the item indexed at 0.