LABjs-2.0.3

代码说明：

  LABjs 的核心是 LAB（Loading and Blocking）：Loading 指异步并行加载，Blocking 是指同步等待执行。LABjs 通过优雅的语法（script 和 wait）实现了这两大特性，核心价值是性能优化。LABjs 是一个文件加载器。(LABjs lets you load pretty much any script file, whether you control it or not, with no intrusion or convention for dependencies, other than the order and blocking that you define. It keeps track of what you ve asked for and what has downloaded, and lets you only define a handler once for a group of scripts that will execute together in parallel. The API style (with chaining) makes is very easy to convert a set of script tags in your page into code to load them, without having to worry that race conditions will cause issues for scripts loading in the wrong order if there are explicit dependencies involved.)