为什么console.log在分配之前会记录一个值？

Question

A short example:

self.curTabs = null;

$j.getJSON(url)
    .done(function (response) {
        self.curTabs = response.tabs;

        _.each(self.curTabs, function (tab) {
            tab.dataLoaded = true;
        });

        console.log(self.curTabs);
    });

Logical output: [ 0: Object { dataLoaded: true, etc... }, 1: etc... ] .

But with this example:

self.curTabs = null;

$j.getJSON(url)
    .done(function (response) {
        self.curTabs = response.tabs;

        _.each(self.curTabs, function (tab) {
            tab.dataLoaded = true;
        });

        console.log(self.curTabs);

        _.each(self.curTabs, function (tab) {
            tab.dataLoaded = false;
        });
    });

Illogical output: [ 0: Object { dataLoaded: false, etc... }, 1: etc... ] .

Why the variable get the value false before I assign it?

Answer 1

Because console.log isn't synchronous in every implementation. That way it's queued till the main thread finished. In the meantime your new value is set.