Node.js util.format（）作为String.prototype

Question

I am trying to create/extend the node.js util.format function so that it can be used as a prototype (eg: "Hello %s".format("World")). However, I have been unsuccessful trying it. I have tried the following formats to no avail:

String.prototype.format = function(){return util.format(this, arguments)};

and

String.prototype.format = function(){return util.format.apply(this, arguments)};

and also

String.prototype.format = function(args){return util.format(this, args)};

None of these work. Do you have any idea what I am doing wrong?

Thanks, Manuel

Answer 1

I assume you would be calling it like this?

"%s: %s".format('key', 'val');

like this:

String.prototype.format = function(){
  var args = Array.prototype.slice.call(arguments);
  args.unshift(this.valueOf());
  return util.format.apply(util, args);
};

In your first example, you are only passing 2 arguments, the format string, and the arguments object. You get closer with your second attempt, but the context of format should probably be util . You need to add this to the set of arguments applied to format . Also when working with this on a string, you are working with the string Object, not the string literal, so you must get the literal version using valueOf .