What's this JavaScript syntax with the "$" and "[]"?

Question

I am learning jQuery. The code snippet as below. I don't understand the syntax of the last statement.

Why there's no .?
what does the [] mean?

BTW, what's special with the $?

/* Code provided for context, irrelevant to the actual question.
  $('#executeButton').click(function(){
  $('body').addClass('done');
  $('.done #controls :radio').attr('disabled',true);
  var sources$ = $('#sourcePane input:checked~img');
  if ($('[name=clone]:checked').val()=='yes') sources$ = sources$.clone();
  var targets$ = $('#targetPane input:checkbox:checked').parents('.target');
  var operation = $('[name=operations]:checked').val();*/
  targets$[operation](sources$); //<=== HERE
/*});*/

And some more context:

    <div>
      <label>Operation:</label><br/>
      <input type="radio" name="operations" value="append" checked="checked"/> append
      <input type="radio" name="operations" value="prepend"/> prepend
      <input type="radio" name="operations" value="before"/> before
      <input type="radio" name="operations" value="after"/> after
    </div>

The variable names most likely have had a `$` put in it to indicate that the variable contains a jQuery object. — Marc Harry, Nov 30 '15 at 09:09
Let's see this line: `targets$[operation](sources$);` The `targets$` and `sources$` are simply variables. `$` is a valid character that can be used anywhere in the variable, like how you can use `S`. Changing them to `targetsS` or `sourcesS` mean the same. The `targets$[operation]` is an array index. The `targets$` is already an array that selects all the checked checkbox containing `.target`. — Praveen Kumar Purushothaman, Nov 30 '15 at 09:10
window.jQuery = window.$ = jQuery; in short its a alias to call jQuery function on the other hand , targets$ is just fancy variable name because you can have special character in your variable names it doesnot realates to jquery function — Suraj Rawat, Nov 30 '15 at 09:12
Nothing weird here. That's ordinary jQuery, "$" sign can be used in variables like any other character, as long as it's not the first one. See [here](http://jsfiddle.net/yahavbr/b2La2Lfr/) for example — Shadow The GPT Wizard, Nov 30 '15 at 09:12
May be this one. http://stackoverflow.com/questions/17189642/difference-between-using-bracket-and-dot-notation — Bhojendra Rauniyar, Nov 30 '15 at 09:15

score 3 · Accepted Answer · answered Nov 30 '15 at 09:10

3

what does the [] mean?

[] is a special javascript property access notation . imagine if i have an ojbect like:

var o =  {
   "abc.xyz" : 5
};

I can't say o.abc.xyz , that's where [] is handy o['abc.xyz'].

What's special with the $?

$ is often used as a naming convention with jquery for examle:

var $this = $(this);

answered Nov 30 '15 at 09:10

Ramanlfc

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I only see a wrapset method invoked with a `.` like `$(*).append(...)`. I didn't know that it can be called like this `$(*)[append](...)`. – smwikipedia Nov 30 '15 at 09:19
@smwikipedia: in `$(*)[append](...)`, `append` is a variable name. This works, for example: `var a = "append"; $("*")[a]()`. The variable should contain the function's _name_. – Cerbrus Nov 30 '15 at 09:21
@Cerbrus I guess you mean `$('*')['append'](...)` or `var a = 'append'; $('*')[a](...)`. – smwikipedia Nov 30 '15 at 09:25
1

`[a]`, indeed. Whoops. – Cerbrus Nov 30 '15 at 09:26
My confusion is not caused by something like `$('[name=x]')`. I am just not fully *adjusted* to the syntax to invoke a method as a property with `[]`. Well I think that's forgivable after only 2 day's crash learning of jQuery without any JS experience. This answer catches my pain point. At the price of so many down-votes, I guess it won't be easily forgotten. :) – smwikipedia Nov 30 '15 at 09:35

score 1 · Answer 2 · answered Nov 30 '15 at 09:12

Let's see this line:

targets$[operation](sources$);

The targets$ and sources$ are simply variables. $ is a valid character that can be used anywhere in the variable, like how you can use S. Changing them to targetsS or sourcesS mean the same.

The targets$[operation] is an array index. The targets$ is already an array that selects all the checked checkbox containing .target.

What's this JavaScript syntax with the "$" and "[]"?

2 Answers2