How to create partial method in javascript

14 November 2013

	Function.prototype.partial = function() {
		var fn = this,
			args = Array.prototype.slice.call(arguments);

		function preparForArgs(newArgs) {
				var arg = 0,
					i,
					l;
				for(i=0,l=args.length; i<l; i++) {
					if(args[i] == undefined) {
						args[i] = newArgs[arg++];
					}
				}
		}
		return function() {

			preparForArgs(arguments);
			return fn.apply(this, args);
		}
	};

first we create partial method on the Function’s prototype, that make all the function able to partial.

var fn = this;

use fn to save the origial function, args to save the original parameters.

preparForArgs, is to create new arguments for the partial function, use undefined as a placeholder, if we see undefined, then get the arguemnt from newly passed arguments.

	var delay = setTimeout.partial(undefined, 1000);

	delay(function() {
		alert('delayed');
	});

we can create a new delay function base on setTimeout function. and use undefined as the placeholder.

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