localStorage sessionStorage 增强版

;(function() {
            const api = {
                setItem(key, val) {
                    if (tip(arguments, ‘setItem‘, 2)) { return }
                    this.storage.setItem(key, serialize(val))
                    return val
                },

                getItem(key, defaultVal) { 
                    if (tip(arguments, ‘getItem‘, 1)) { return }
                    // 如果没有该key, 则自动设置到缓存中去, 默认值为null
                    if (!this.has(key)) {
                        return this.setItem(key, null)
                    }
                    let ret = deserialize(this.storage.getItem(key))
                    // 如果有该key,但是值为undefined或者null,则使用默认值且设置到缓存去
                    if (defaultVal && (ret === undefined || ret === null)) {
                        ret = this.setItem(key, defaultVal)
                    }
                    return ret
                },

                removeItem(key) {
                    if (tip(arguments, ‘removeItem‘, 1)) { return }
                    this.storage.removeItem(key)
                },

                clear() {
                    this.storage.clear()
                },

                key(index) {
                    if (tip(arguments, ‘key‘, 1)) { return }
                    this.storage.key(index)
                },

                has(key) {
                    if (tip(arguments, ‘has‘, 1)) { return }
                    // 使用原生getItem方法,如果没有该key会返回字符串"null"
                    return this.storage.getItem(key) !== null
                },

                getAll() {
                    let map = Object.create(null)
                    this.forEach((key, val) => {
                        map[key] = val
                    })
                    return map
                },

                forEach(callback, ctx) {
                    for (let i = 0; i < this.storage.length; i++) {
                        let key = this.storage.key(i)
                        callback && callback.call(ctx, key, this.getItem(key), i)
                    }
                }
            }

            let local = Object.assign({
                storage: window.localStorage
            }, api)

            let session = Object.assign({
                storage: window.sessionStorage
            }, api)

            function serialize(val) {
                return JSON.stringify(val)
            }

            function deserialize(val) {
                try {
                    return JSON.parse(val)
                } catch (e) {
                    return val === "undefined" ? undefined : val
                }
            }

            function tip(args, operation, actualNum) {
                if (args.length < actualNum) {
                    console.error(
                        `Failed to execute ‘${operation}‘ on ‘store‘: ${actualNum} arguments required, but only ${args.length} present.`
                    )
                    return true;
                } else {
                    return false;
                }
            }

            if (
                typeof module !== ‘undefined‘ && 
                typeof exports === ‘object‘
            ) {
                module.exports = { local, session }
            } else {
                window.local = local
                window.session = session
            }
        })();

        // 原生
        localStorage.setItem(‘num‘, 1)
        localStorage.setItem(‘str‘, ‘str‘)
        localStorage.setItem(‘arr‘, [1, 2, 3])
        localStorage.setItem(‘obj‘, {a: 1, b: 2, c: 3})
        localStorage.setItem(‘undefined‘, undefined)
        localStorage.setItem(‘null‘, null)

        console.log(localStorage.getItem(‘test‘), Object.prototype.toString.call(localStorage.getItem(‘test‘)))
        console.log(localStorage.getItem(‘num‘), Object.prototype.toString.call(localStorage.getItem(‘num‘)))
        console.log(localStorage.getItem(‘str‘), Object.prototype.toString.call(localStorage.getItem(‘str‘)))
        console.log(localStorage.getItem(‘arr‘), Object.prototype.toString.call(localStorage.getItem(‘arr‘)))
        console.log(localStorage.getItem(‘obj‘), Object.prototype.toString.call(localStorage.getItem(‘obj‘)))
        console.log(localStorage.getItem(‘undefined‘), Object.prototype.toString.call(localStorage.getItem(‘undefined‘)))
        console.log(localStorage.getItem(‘null‘), Object.prototype.toString.call(localStorage.getItem(‘null‘)))


        // 增强版
        local.setItem(‘__num__‘, 1)
        local.setItem(‘__str__‘, ‘str‘)
        local.setItem(‘__arr__‘, [1, 2, 3])
        local.setItem(‘__obj__‘, {a: 1, b: 2, c: 3})
        local.setItem(‘__undefined__‘, undefined)
        local.setItem(‘__null__‘, null)

        console.log(local.getItem(‘__test__‘), Object.prototype.toString.call(local.getItem(‘__test__‘)))
        console.log(local.getItem(‘__num__‘), Object.prototype.toString.call(local.getItem(‘__num__‘)))
        console.log(local.getItem(‘__str__‘), Object.prototype.toString.call(local.getItem(‘__str__‘)))
        console.log(local.getItem(‘__arr__‘), Object.prototype.toString.call(local.getItem(‘__arr__‘)))
        console.log(local.getItem(‘__obj__‘), Object.prototype.toString.call(local.getItem(‘__obj__‘)))
        console.log(local.getItem(‘__undefined__‘), Object.prototype.toString.call(local.getItem(‘__undefined__‘)))
        console.log(local.getItem(‘__null__‘), Object.prototype.toString.call(local.getItem(‘__null__‘)))