HTML5 localStorage 有用的函数 // JavaScript、TypeScript

HTML5 localStorage useful Functions // JavaScript, TypeScript

提问by CoderPi

How to: *

如何： *

• Check if localStorageis supported
• Check if localStoragehas an Item
• Get the amount of space left in localStorage
• Get the maximum amount of space in localStorage
• Get the used space in localStorage
• Get a Backup of localStorage
• Apply a Backup to localStorage
• Dump all information of localStoragein the console

• 检查是否localStorage支持
• 检查是否localStorage有项目
• 获取剩余的空间量 localStorage
• 获得最大的空间量 localStorage
• 获取已用空间 localStorage
• 获取备份 localStorage
• 将备份应用到 localStorage
• 转储localStorage控制台中的所有信息

*check the answers below

*检查下面的答案

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FAQ:

常问问题：

• [link]How to store Objects in localStorage
• [link]How to store an Array in localStorage
• [link]How to save an Image in localStorage
• [link]localStorageTutorial (also covers storage eventsand things to remember)

• [链接]如何将对象存储在localStorage
• [链接]如何将数组存储在localStorage
• [链接]如何将图像保存在localStorage
• [链接]localStorage教程（还包括存储事件和要记住的事情）

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Related:

有关的：

• [link]General Information about Web Storage
• [link]sessionStoragedata stored gets cleared when the page session ends
• [link]indexedDBa low-level API for client-side storage of structured data

• [链接]关于网络存储的一般信息
• [链接]sessionStorage当页面会话结束时，存储的数据被清除
• [链接]indexedDB用于客户端存储结构化数据的低级 API

回答by CoderPi

My suite of functions for localStoragein JavaScript and TypeScript

我的localStorageJavaScript 和 TypeScript函数套件

• isSupported
• hasItem(key)
• getSpaceLeft()
• getMaximumSace()
• getUsedSpace()
• getItemUsedSpace()
• getBackup()
• applyBackup(backup, fClear, fOverwriteExisting)
• consoleInfo(fShowMaximumSize)

• isSupported
• hasItem(key)
• getSpaceLeft()
• getMaximumSace()
• getUsedSpace()
• getItemUsedSpace()
• getBackup()
• applyBackup(backup, fClear, fOverwriteExisting)
• consoleInfo(fShowMaximumSize)

The complete code as LocalStorage-Module on GitHubGist: JavaScriptand TypeScript
Live example: on JSFiddle

LocalStorageGitHubGist 上的 -Module 完整代码：JavaScript和TypeScript
现场示例：JSFiddle

Check if localStorage is supported - TypeScript-Version

检查是否支持 localStorage - TypeScript-Version

/**
  * Flag set true if the Browser supports localStorage, without affecting it
  */
var localStorage_isSupported = (function () {
    try {
        var itemBackup = localStorage.getItem("");
        localStorage.removeItem("");
        localStorage.setItem("", itemBackup);
        if (itemBackup === null)
            localStorage.removeItem("");
        else
            localStorage.setItem("", itemBackup);
        return true;
    }
    catch (e) {
        return false;
    }
})();

Check if localStorage has an Item - TypeScript-Version

检查 localStorage 是否有一个项目 - TypeScript-Version

/**
 * Check if localStorage has an Item / exists with the give key
 * @param key the key of the Item
 */
function localStorage_hasItem(key) {
    return localStorage.getItem(key) !== null;
}

Get the amount of space left in localStorage - TypeScript-Version

获取 localStorage 中剩余的空间量 - TypeScript-Version

/**
 * This will return the left space in localStorage without affecting it's content
 * Might be slow !!!
 */
function localStorage_getRemainingSpace() {
    var itemBackup = localStorage.getItem("");
    var increase = true;
    var data = "1";
    var totalData = "";
    var trytotalData = "";
    while (true) {
        try {
            trytotalData = totalData + data;
            localStorage.setItem("", trytotalData);
            totalData = trytotalData;
            if (increase)
                data += data;
        }
        catch (e) {
            if (data.length < 2) {
                break;
            }
            increase = false;
            data = data.substr(data.length / 2);
        }
    }
    if (itemBackup === null)
        localStorage.removeItem("");
    else
        localStorage.setItem("", itemBackup);
    return totalData.length;
}

Get the maximum amount of space in localStorage - TypeScript-Version

获取 localStorage 中的最大空间量 - TypeScript-Version

/**
 * This function returns the maximum size of localStorage without affecting it's content
 * Might be slow !!!
 */
function localStorage_getMaximumSize() {
    var backup = localStorage_getBackup();
    localStorage.clear()
    var max = localStorage_getRemainingSpace();
    localStorage_applyBackup(backup);
    return max;
}

Get the used space in localStorage - TypeScript-Version

获取 localStorage 中的已用空间 - TypeScript-Version

/**
 * This will return the currently used size of localStorage
 */
function localStorage_getUsedSize() {
    var sum = 0;
    for (var i = 0; i < localStorage.length; ++i) {
        var key = localStorage.key(i)
        var value = localStorage.getItem(key);
        sum += key.length + value.length;
    }
    return sum;
}

Get the space used my an Item TypeScript-Version

获取我的项目TypeScript-Version使用的空间

/**
 * This will return the currently used size of a given Item,returns NaN if key is not found
 * @param key
 */
function getItemUsedSpace(key) {
    var value = localStorage.getItem(key);
    if (value === null) {
        return NaN;
    }
    else {
        return key.length + value.length;
    }
}

Backup Assosiative Array, only TypeScript-Version

备份关联数组，仅TypeScript 版本

Get a Backup of localStorage - TypeScript-Version

获取 localStorage 的备份 - TypeScript-Version

/**
 * This will return a localStorage-backup (Associative-Array key->value)
 */
function localStorage_getBackup() {
    var backup = {};
    for (var i = 0; i < localStorage.length; ++i) {
        var key = localStorage.key(i);
        var value = localStorage.getItem(key);
        backup[key] = value;
    }
    return backup;
}

Apply a Backup to localStorage - TypeScript-Version

将备份应用到 localStorage - TypeScript-Version

/**
 * This will apply a localStorage-Backup (Associative-Array key->value)
 * @param backup            associative-array 
 * @param fClear             optional flag to clear all existing storage first.Default:true
 * @param fOverwriteExisting optional flag to replace existing keys. Default: true
 */
function localStorage_applyBackup(backup, fClear, fOverwriteExisting) {
    if (fClear === void 0) { fClear = true; }
    if (fOverwriteExisting === void 0) { fOverwriteExisting = true; }
    if (fClear == true) {
        localStorage.clear();
    }
    for (var key in backup) {
        if (fOverwriteExisting === false && backup[key] !== undefined) {
            continue;
        }
        var value = backup[key];
        localStorage.setItem(key, value);
    }
}

Dump all information of localStorage in the console - TypeScript-Version

在控制台转储 localStorage 的所有信息 - TypeScript-Version

/**
 * This functions dumps all keys and values of the local Storage to the console,
 * as well as the current size and number of items
 * @param fShowMaximumSize optional, flag show maximum size of localStorage. Default: false
 */
function localStorage_consoleInfo(fShowMaximumSize) {
    if (fShowMaximumSize === void 0) { fShowMaximumSize = false; }
    var amount = 0;
    var size = 0;
    for (var i = 0; i < localStorage.length; ++i) {
        var key = localStorage.key(i)
        var value = localStorage.getItem(key);
        console.log(amount, key, value);
        size += key.length + value.length;
        amount++;
    }
    console.log("Total entries:", amount);
    console.log("Total size:", size);
    if (fShowMaximumSize === true) {
        var maxSize = localStorage_getMaximumSize();
        console.log("Total size:", maxSize);
    }
}

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Notes

笔记

• Each key and value is using the exact amount of space equal to its string length
• The maximum storage-space allowed in my tests: ~5MB
  • 5000000 Edge
  • 5242880 Chrome
  • 5242880 Firefox
  • 5000000 IE
• Firefox issue:Don't use for (var key in localStorage)but: for (var i = 0; i < localStorage.length; ++i) { var key = localStorage.key(i). The for..in-loop it would give the localStorageMemberfunctions as keys

• 每个键和值都使用与其字符串长度相等的确切空间量
• 我的测试中允许的最大存储空间：~5MB
  • 5000000 边缘
  • 5242880 铬
  • 5242880 火狐
  • 5000000 IE
• Firefox 问题：不要使用for (var key in localStorage)但是： for (var i = 0; i < localStorage.length; ++i) { var key = localStorage.key(i)。该for..in-loop它会给localStorageMemberfunctions为key小号

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// Example - http://jsfiddle.net/1rqtd7pg/1/

// 示例 - http://jsfiddle.net/1rqtd7pg/1/

console.log("LocalStorage supported:", LocalStorage.isSupported)
// true - I hope so anyways 
if(LocalStorage.isSupported) {
    localStorage.setItem("asd", "ASDASD")                           
    // sets / overwrites the item "asd"
    localStorage.setItem("asd" + Math.random(), "ASDASD")           
    // set another item each time you refresh the page
    var backup = LocalStorage.getBackup()                           
    // creates a backup, we will need it later!
    console.log(JSON.stringify(backup))                             
    // this is how the backup looks like
    var usedSpace = LocalStorage.getUsedSpace()                     
    // amount of space used right now
    console.log("Used Space:", usedSpace)
    var maxSpace = LocalStorage.getMaximumSpace()                   
    // amount of maximum space aviable
    console.log("Maximum Space:", maxSpace)
    var remSpace = LocalStorage.getRemainingSpace()                 
    // amount of remaining space
    console.log("Remaining Space:", remSpace)
    console.log("SpaceCheck", maxSpace === usedSpace + remSpace)    
    // true
    console.log("hasItem", LocalStorage.hasItem("nothis0ne"))       
    // we don't have this one in our localStorage
    localStorage.clear()                                            
    // oops, we deleted the localStorage!
    console.log("has asd", LocalStorage.hasItem("asd"))              
    // item asd is lost 
    LocalStorage.applyBackup(backup)                                
    // but we have a backup, restore it!
    LocalStorage.consoleInfo()                                      
    // show all the info we have, see the backup worked 
}