HTML5本地存储有用函数//JavaScript，类型脚本 [英] HTML5 localStorage useful Functions // JavaScript, TypeScript

问题描述

如何操作：*

• 检查是否支持localStorage
• 检查localStorage是否有项目
• 获取localStorage中的剩余空间量
• 获取localStorage中的最大空间量
• 获取localStorage中的已用空间
• 获取localStorage的备份
• 将备份应用于localStorage
• 将localStorage的所有信息转储到控制台

*检查下面的答案

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常见问题解答：

• [link]localStorage
如何存储对象
• [link]如何在localStorage
中存储数组
• [link]如何在localStorage中保存图像
• [link]localStorage教程(还介绍存储事件和注意事项)

---

相关：

• [link]Web存储一般信息
• [link]sessionStorage页面会话结束时清除存储的数据
• [link]indexedDB结构化数据客户端存储底层API

推荐答案

我在JavaScript和TypeScript中的localStorage函数套件

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

完整代码为LocalStorage-GitHubGist上的模块：JavaScript和TypeScript
现场示例：在JSFiddle

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;
    }
})();

检查localStorage是否有项-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;
}

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;
}

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;
}

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;
}

获取我的项目已用空间TypeScript-Version

/**
 * 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;
    }
}

备份关联数组，仅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;
}

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);
    }
}

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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备注

• 每个键和值使用的空间量与其字符串长度完全相同
• 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)。for..in-循环会将localStorage成员函数指定为keys

---

//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 😊
}

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