A problem related to currying, [this] .concat ([] .slice.call (arguments)) does not understand this sentence?

topic description

The

function asyncify is a function whose output is the same regardless of whether it is called asynchronously or called by Synchronize (in this case, a = 1). The judgment about Synchronize does not quite understand the logical meaning of it, especially the statement [this] .concat ([] .slice.call (arguments). The book explains that this is called currying, later, which roughly means that parameters can be passed in succession. Later, I still didn"t understand this sentence

sources of topics and their own ideas

A case study of the callback chapter in the book "JavaScript you don"t know"

related codes

function asyncify(fn) {
      var orig_fn = fn,
          intv = setTimeout(function () {
                    intv = null;
                    if (fn) fn();
                 }, 0);
      console.log("Wai intv:"+intv);
      fn = null;
      return function () {
        console.log("Nei intv:"+intv);
        if (intv) {
          // 
          fn = orig_fn.bind.apply(
            orig_fn,
            // thisbind(..)
            // currying
            [this].concat([].slice.call(arguments))  
          );
        } else {
          // 
          orig_fn.apply(this, arguments); 
        }
      };
    }
    function result(data) {
      console.log(a); 
    }

    var a = 0;
    var b = asyncify(result);
    aPP;