How jQuery distinguish between 'data' and 'selector' parameter?
in jQuery function:
.on(event, [selector,] [data,] handler)
How jQuery parse this call:
on('click', 'tag3', () => {})
tag3 is selector or data ?
The last argument must be the handler. So if there are two arguments there there is no data and no selector .
If there are four arguments than the second one must be selector and the third one must be data .
So it only becomes tricky if there are exactly three arguments.
If the second argument isn't a string, then it can't be a selector, so it must be data.
If it is a string then it could be a selector or data. Now jQuery could do some heuristics by running it through the selector engine and seeing if it is a valid selector … but it doesn't. It just assumes that if the second argument is a string then it is a selector.
How jQuery distinguish between 'data' and 'selector' parameter?
They have a different data-types
data - is a plain object (not a DOM or jquery object)
selector - is a string or a jquery/DOM/DOM-array object.
so, jquery can make out whether an argument is a selector or data by judging the properties of the argument, for example this and this
return obj instanceof HTMLElement; //to check if it is a DOM object
or
return obj instanceof jQuery; //to check if it is a jquery object
tag3 is selector or data?
As per documentation
If a string is passed as the parameter to $(), jQuery examines the string to see if it looks like HTML (ie, it starts with ). If not, the string is interpreted as a selector expression, as explained above. But if the string appears to be an HTML snippet, jQuery attempts to create new DOM elements as described by the HTML. Then a jQuery object is created and returned that refers to these elements.
If the string passed to jquery method is an HTML then subsequent object is either a document (DOM object) or an attributes object.
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