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This commit is contained in:
Ilya Kantor 2019-05-19 23:05:25 +03:00
parent b52dd6fd7b
commit 5c6a3f003f
2 changed files with 12 additions and 10 deletions
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6-data-storage/02-localstorage/article.md
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@ -7,7 +7,7 @@ What's interesting about them is that the data survives a page refresh (for `ses
We already have cookies. Why additional objects?
- Unlike cookies, web storage objects are not sent to server with each request. Because of that, we can store much more. Most browsers allow at least 2 megabytes of data (or more) and have settings to configure that.
- The server can't manipulate storage objects via HTTP headers, everything's done in JavaScript.
- Also unlike cookies, the server can't manipulate storage objects via HTTP headers. Everything's done in JavaScript.
- The storage is bound to the origin (domain/protocol/port triplet). That is, different protocols or subdomains infer different storage objects, they can't access data from each other.
Both storage objects provide same methods and properties:
@ -19,6 +19,8 @@ Both storage objects provide same methods and properties:
- `key(index)` -- get the key on a given position.
- `length` -- the number of stored items.
As you can see, it's like a `Map` colection (`setItem/getItem/removeItem`), but also keeps elements order and allows to access by index with `key(index)`.
Let's see how it works.
## localStorage demo
@ -71,11 +73,11 @@ That's allowed for historical reasons, and mostly works, but generally not recom
## Looping over keys
Methods provide get/set/remove functionality. But how to get all the keys?
As we've seen, the methods provide get/set/remove functionality. But how to get all saved values or keys?
Unfortunately, storage objects are not iterable.
One way is to use "array-like" iteration:
One way is to loop over them as over an array:
```js run
for(let i=0; i<localStorage.length; i++) {
@ -84,9 +86,9 @@ for(let i=0; i<localStorage.length; i++) {
}
```
Another way is to use object-specific `for key in localStorage` loop.
Another way is to use `for key in localStorage` loop, just as we do with regular objects.
That iterates over keys, but also outputs few built-in fields that we don't need:
It iterates over keys, but also outputs few built-in fields that we don't need:
```js run
// bad try