定義:
前提:假設一段代碼分如下3步
{
//step1
.....
//step2 [耗時操作]
.....
//step3
.....
}
1、同步-代碼邏輯嚴格按照順序依次執行,那麼代碼執行順序step1->step2->step3
2、異步-為達到異步效果,我們單獨為step2開啟一個線程處理該邏輯,那麼代碼執行順序很極有可能為step1-.step3->step2,JS中的回調就是常見的應用
舉例(JS):
同步:
var result = database.query("SELECT * FROM hugetable");
console.log("Query finished");
console.log("Next line");
輸出:
Query finished
Next line
異步:
database.query("SELECT * FROM hugetable", function(result) {
console.log("Query finished");
});
console.log("Next line");
輸出:
Next line
Query finished