github-files.js

;(function ($) {
  var githubCacheFilePath = [];
  var githubCacheSha = [];

  var fnSuccess =
    function (data, startLineNum, endLineNum, callback) {
      if (data.data.content && data.data.encoding === "base64") {
        var contentArray = 
          window
            .atob(data.data.content.replace(/\n/g, ""))
            .split("\n");

        endLineNum = endLineNum || contentArray.length;

        callback(contentArray.slice(startLineNum - 1, endLineNum).join("\n"));
      }
    };

  $.getGithubFileByFilePath =
    function(user, repo, filePath, callback, startLineNum, endLineNum) {
      if(githubCacheFilePath[filePath]){
          $.getGithubFile(user, repo, githubCacheFilePath[filePath], callback, startLineNum, endLineNum)
      }else{
        $.ajax({
          type: "GET"
          ,url: "https://api.github.com/repos/" + user + "/" + repo + "/contents/"+filePath
          ,dataType: "jsonp"
          ,success: function(data){
            githubCacheFilePath[filePath] = data.data.sha;
            $.getGithubFile(user, repo, githubCacheFilePath[filePath], callback, startLineNum, endLineNum)
          }
        });
      }
    };

  $.getGithubFile =
    function(user, repo, sha, callback, startLineNum, endLineNum) {
      if(githubCacheSha[sha]){
        fnSuccess(githubCacheSha[sha], +startLineNum || 1, +endLineNum || 0, callback);
      }else{
        $.ajax({
          type: "GET"
          ,url: "https://api.github.com/repos/" + user + "/" + repo + "/git/blobs/" + sha
          ,dataType: "jsonp"
          ,success: function(data) {
            githubCacheSha[sha] = data
            fnSuccess(githubCacheSha[sha], +startLineNum || 1, +endLineNum || 0, callback);
          }
        });
      }
    };
}(jQuery));