js缓存计算

本文探讨了JavaScript中如何利用缓存提高计算性能,通过案例分析了缓存技术在处理复杂运算或重复调用时的优势,旨在帮助开发者优化代码,提升网页应用的响应速度。
//Memoized
var fibonacci=function(){
  var memo=[0,1];
  var fib = function(n){
    var result=memo[n];
    if(typeof result != 'number'){
      result = fib(n-1) + fib(n-2);
      memo[n]=result;
    }
    return result;
  };
  return fib;
}();

或者

var fibArr = [ 0, 1, 1];
(function fibonacci(n){
    var ind = fibArr[n];
    return ind ? ind : (fibArr[n] = fibonacci(n-1) + fibonacci(n-2))
})(50);


//nomemoized
var fib = function(n){
    return n<2 ? n : fib(n-1)+fib(n-2);
}


for(var i=0;i<10;i++){//改成50次差不多炸
console.log(i+" "+fib(i));  
}

for(var i=0;i<10;i++){
console.log(i+" "+fibonacci(i));  
}
<think>Hmm, the user is asking about how to calculate cache in UniApp specifically. Looking at the provided references, there are multiple code snippets showing different approaches. References [2] and [3] both demonstrate using plus.cache.calculate() method to get cache size, but with slight variations in implementation. The key steps seem to be: 1. Calling plus.cache.calculate() 2. Getting the size in bytes 3. Converting to human-readable formats (B, KB, MB, GB) The user seems focused specifically on the calculation part, not the cleanup process mentioned in reference [4]. They're probably implementing a feature to display cache size in their UniApp project. Noticed all references use the same core method but have different variable names and formatting details. The essential pattern is consistent though: - plus.cache.calculate() gets the raw byte count - Conditional formatting based on size thresholds - toFixed(2) for decimal precision in larger units The Android/iOS distinction in reference [4] isn't relevant here since cache calculation works the same across platforms. Should keep the answer focused purely on measurement. </think>以下是UniApp中计算缓存的具体方法及实现步骤,参考官方文档和最佳实践: ### 核心方法:`plus.cache.calculate()` ```javascript methods: { // 计算缓存大小 calculateCache() { plus.cache.calculate(size => { const bytes = parseInt(size); let result = ""; if (bytes < 1024) { result = bytes + "B"; } else if (bytes < 1048576) { // 1024*1024 result = (bytes / 1024).toFixed(2) + "KB"; } else if (bytes < 1073741824) { // 1024*1024*1024 result = (bytes / 1048576).toFixed(2) + "MB"; } else { result = (bytes / 1073741824).toFixed(2) + "GB"; } console.log("当前缓存:", result); this.cacheSize = result; // 绑定到页面数据 }); } } ``` ### 实现步骤 1. **调用缓存API**:使用`plus.cache.calculate()`获取字节单位的缓存大小 2. **单位转换**: - `1024B = 1KB` - `1048576B = 1MB`(1024×1024) - `1073741824B = 1GB`(1024³) 3. **保留小数**:通过`.toFixed(2)`保留两位小数 4. **数据绑定**:结果赋值给Vue数据对象,实现页面动态更新 ### 完整示例(Vue页面) ```html <template> <view> <text>缓存大小: {{cacheSize}}</text> <button @click="calculateCache">计算缓存</button> </view> </template> <script> export default { data() { return { cacheSize: "0B" // 初始值 } }, methods: { calculateCache() { plus.cache.calculate(size => { const bytes = parseInt(size); // 单位转换逻辑同上 }); } } } </script> ``` ### 注意事项 1. **平台兼容性**:此方法在Android/iOS均适用,无需平台判断[^2][^3] 2. **异步回调**:计算结果通过回调函数返回,需异步处理 3. **权限要求**:Android需添加`<uses-permission android:name="android.permission.GET_PACKAGE_SIZE"/>` 4. **精度问题**:大文件场景建议使用MB/GB单位避免小数位溢出 > 此实现基于UniApp的HTML5+扩展规范,实际缓存包含应用数据、临时文件等[^1][^4]。
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