js单线程执行

console.log("111");
foo(function () {
    console.log("222");
});
console.log("333");


function foo(callback) {
    process.nextTick(function () {
        callback();
    })
}

111
333
222

console.log("111");
foo(function () {
    console.log("222");
});
console.log("333");


function foo(callback) {
    callback();
}

111
222
333