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40 changes: 22 additions & 18 deletions week_10_angular_and_reviews/day_04_more_js/presentations/emmy_localStorage.md
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Original file line number Diff line number Diff line change
Expand Up @@ -2,33 +2,35 @@

##WHY
Cookie limitations
Included in every HTTP request (slows down apps, less secure)
Limited amount of date
* Included in every HTTP request (slows down apps, less secure)
* Limited amount of date

We’re spoiled because this type of thing used to be a lot harder #youths

##WHAT
Local storage offers more storage space, on the client side, that persists beyond a page refresh and isn’t transmitted to the server.

Unlike session storage, local storage stays after a browser is quit (aka is persistent).

##WHERE
Where is all of this data going!?

You can view/delete local storage entries using some browsers. Here is a youtube demo with chrome. Essentially go Chrome > preferences > privacy > content settings > cookies > show cookies and other data. You see a list of cookies stored on your computer.

##HOW
Mini-example: counting the number of times a user has visited a page

`<p>You have viewed this page <span id="count">an untold number of</span> time(s).</p>`

`<script>`

```
if(!localStorage.pageLoadCount) {
localStorage.pageLoadCount = 0;
}
localStorage.pageLoadCount = parseInt(localStorage.pageLoadCount) + 1;
document.getElementById('count').textContent = localStorage.pageLoadCount;
```
`</script>`
<p>You have viewed this page <span id="count">an untold number of</span> time(s).</p>`

<script>

if(!localStorage.pageLoadCount) {
localStorage.pageLoadCount = 0;
}
localStorage.pageLoadCount = parseInt(localStorage.pageLoadCount) + 1;
document.getElementById('count').textContent = localStorage.pageLoadCount;

</script>

localStorage is a JavaScript object and an extension of Storage. (like sessionStorage)
can think of it as an object of key-value pairs.
Expand All @@ -45,8 +47,10 @@ localStorage["bar"] = foo;
```

Important: note that data is stored as strings. You can get around this using some JSON.

**have array ‘names’ you want to store**
`localStorage[“names”] = JSON.stringify(names);`

**want to use it again**
`var storedNames = JSON.parse(localStorage[“names"];`

Expand All @@ -64,7 +68,7 @@ Alternative: Indexed Database API = api for key-value data management. uses tran

##USES
A bit obvious, but...
if your page renders a lot of data (like a google map), can store the data locally on someone’s comp upon first page load. Then reloading the page will happen instantly.
Store form data if a user has made some entries but hasn’t submitted yet.
Maintain the state of a game even if browser is closed.
Know when it’s a user’s first visit to a site and render the page accordingly.
* if your page renders a lot of data (like a google map), can store the data locally on someone’s comp upon first page load. Then reloading the page will happen instantly.
* Store form data if a user has made some entries but hasn’t submitted yet.
* Maintain the state of a game even if browser is closed.
* Know when it’s a user’s first visit to a site and render the page accordingly.