Function.prototype.bind = function(that){
var self = this,
args = arguments.length > 1 ? Array.slice(arguments, 1) : null,
F = function(){};
var bound = function(){
var context = that, length = arguments.length;
if (this instanceof bound){
F.prototype = self.prototype;
context = new F;
}
var result = (!args && !length)
? self.call(context)
: self.apply(context, args && length ? args.concat(Array.slice(arguments)) : args || arguments);
return context == that ? result : context;
};
return bound;
}, generally use the above method to implement the bind function through ES5 . I don"t quite understand why it is necessary to make such a judgment in the bound function,
if (this instanceof bound) .