JavaScript性能优化策略

// 减少内存使用
var objectPool = [];
var arrayCache = {};
function createObject() {
    if (objectPool.length > 0) {
        return objectPool.pop();
    } else {
        return {};
    }
}
function releaseObject(obj) {
    // do some cleanup
    objectPool.push(obj);
}
function getData(id) {
    if (arrayCache[id]) {
        return arrayCache[id];
    } else {
        var data = fetchData(id);
        arrayCache[id] = data;
        return data;
    }
}
// 减少重绘和回流
var container = document.getElementById("container");
var fragment = document.createDocumentFragment();
for (var i = 0; i < 1000; i++) {
    var div = document.createElement("div");
    div.textContent = "Item " + i;
    fragment.appendChild(div);
}
container.appendChild(fragment);
// 脱离全局作用域
function doSomething() {
    var localVariable = "local";
    // do something with localVariable
}
// 避免使用eval和with
var calculation = Function("a", "b", "return a + b");
var result = calculation(2, 3);
// 使用事件代理
var parentElement = document.getElementById("parent");
parentElement.addEventListener("click", function(event) {
    if (event.target.matches("button")) {
        // handle button click
    }
});
// 使用事件节流和防抖
var button = document.getElementById("button");
var timeoutId;
button.addEventListener("click", function() {
    clearTimeout(timeoutId);
    timeoutId = setTimeout(function() {
        // handle button click after 300ms delay
    }, 300);
});
// 使用性能监测工具
console.time("calculation");
var sum = 0;
for (var i = 0; i < 1000000; i++) {
    sum += i;
}
console.timeEnd("calculation");
// 使用缓存
function heavyCalculation(key) {
    if (heavyCalculation.cache[key]) {
        return heavyCalculation.cache[key];
    } else {
        // do heavy calculation
        var result = ...;
        heavyCalculation.cache[key] = result;
        return result;
    }
}
heavyCalculation.cache = {};
// 代码优化
function calculateSum(array) {
    var sum = 0;
    for (var i = 0; i < array.length; i++) {
        sum += array[i];
    }
    return sum;
}
var numbers = [1, 2, 3, 4, 5];
var sum = calculateSum(numbers);