javascript functions arguments in an array

Question

what I'm trying to do is this

 $.each($(".canvas"), function(n) {
 var canvas = $(this)[0].getContext("2d"); 
 canvas.drawImage(options[n]);
 });

where options would be an array of arguments, but can't figure out how should the array be formatted for it to work

obviously not

['img, 0, 0, 70, 17, 21, 16, 70, 17', 'img, 0, 0, 80, 12, 21, 16, 70, 17']

this neither

[''+img+', 0, 0, 70, 17, 21, 16, 70, 17', ''+img+', 0, 0, 80, 12, 21, 16, 70, 17']

nor this

{0: [img, 0, 0, 70, 17, 21, 16, 70, 17]}

this would not work either

var options = [[img, 0, 0, 70, 17, 21, 16, 70, 17],
 [img, 0, 16, 70, 17, 21, 16, 70, 17],
 [img, 0, 32, 70, 17, 21, 16, 70, 17],
 [img, 0, 48, 70, 17, 21, 16, 70, 17]];
img.onload = function() {
 $.each($(".canvas"), function(n) {
 var canvas = $(this)[0].getContext("2d"); 
 canvas.drawImage(options[n].join(', '));
 });
};

the error is alway Uncaught TypeError: Type error or Uncaught TypeError: Illegal invocation

• Felix Kling: drawImage takes several arguments, not just one which is a string. foo(a, b) is different than foo('a, b'). Only because there a commas in the string does not make it a list of arguments.

Answer 1

Use Function.apply.

canvas.drawImage.apply(canvas, options[n]);

Where options[n] looks something like

[img, 0, 0, 70, 17, 21, 16, 70, 17]

---

Full example:

var options = [[img, 0, 0, 70, 17, 21, 16, 70, 17],
 [img, 0, 16, 70, 17, 21, 16, 70, 17],
 [img, 0, 32, 70, 17, 21, 16, 70, 17],
 [img, 0, 48, 70, 17, 21, 16, 70, 17]];
$(img).load(function()
{
 $(".canvas").each(function(n)
 {
 var canvas = this.getContext('2d'); 
 canvas.drawImage.apply(canvas, options[n]);
 });
});

Demo: http://jsfiddle.net/mattball/5EQbC/

• Felix Kling: options has to have the right structure though. And img must be a DOM element afaik.
• Felix Kling: @foxx: You have to use canvas.drawImage.apply(canvas, options[n]); (pass canvas as first argument).
• fxck: lovely, did try apply() before, but with this instead of canvas, stupid me, thanks