定义:
前提:假设一段代码分如下3步
{
//step1
.....
//step2 [耗时操作]
.....
//step3
.....
}
1、同步-代码逻辑严格按照顺序依次执行,那么代码执行顺序step1->step2->step3
2、异步-为达到异步效果,我们单独为step2开启一个线程处理该逻辑,那么代码执行顺序很极有可能为step1-.step3->step2,JS中的回调就是常见的应用
举例(JS):
同步:
var result = database.query("SELECT * FROM hugetable");
console.log("Query finished");
console.log("Next line");
输出:
Query finished
Next line
异步:
database.query("SELECT * FROM hugetable", function(result) {
console.log("Query finished");
});
console.log("Next line");
输出:
Next line
Query finished