Re-Query Select All the Things!

Remember last week when I spoke about how to use

querySelect()

and

querySelectAll()

and how it could all be done in one command I called

qs()()

? Remember reading the part about how after some research, I've had though about redesigning the function?

Here's what the old version looks like.

var qs = parent => (query,all) => (typeof(parent) === "string") ? qs(qs()(parent))(query,all) : (parent||document)[`querySelector${(all||false)?"All":""}`](query);

And here's the new version of

qs()()

var qs = parent => query => {let q; return (typeof(parent) === "string") ? qs(qs()(parent))(query) : (q = (parent||document).querySelectAll(query)).length > 1 ? q : (q[0]||null);};

Try as I might, I really hoped that that

let q

(or more appropriately

var q

) would have slyly stuck itself into the

q = (parent||document).querySelectorAll(query)

part where assigning

there allows us to have

q.length > 1

without having to put our assignment operation (

) on a separate line with the

let q

statement, but I cannot do that, and here's why.

Remember that when you assign a value to a variable, the assignment operator returns the value assigned to that variable. You can try it out in the debugging console of your browser or in a Node.js console right now. If you type in

five = 5;

the console will return

. That

is stored in the variable

five

until your refresh your browser or exit the Node.js console.

I could go on about operator precedence in JavaScript, but I don't want to.

I could have gone without the

let q

statement and not used the curly braces (

{...}

) and

return

statement as JavaScript variable hoisting would have allowed me to assign a value to

(with

q = (parent||document).querySelectorAll(query)

) without initially declaring

with the

let q

statement but the scope of using the

let

keyword inside a set of parenthesis would not allow me to get

q.length

because if you use

let

var

, or

const

before a variable, it will return

undefined

, and

undefined.length

throws a

TypeError

. And if you are using strict mode, either by putting

"use strict";

at the top of your file or at the beginning of your function, declaring

without

let

var

, or

const

throws a

ReferenceError

// Let's review (assuming strict mode is not initially set in this figure)
five = 5; // => 5 (because the assignment operator returns the value that is assigned to the variable; because strict mode is not enabled, five is hoisted, and can be initialized without declaration first)
var six; // => undefined (declaration keywords (var, let, and const) return undefined even though the variable. If six was previously used, it would have been hoisted.)
var seven = 7; // => undefined (although 7 is assigned to seven; seven is declared and assigned so technically it's hoisted)
var num = x => {
 "use strict";
 let w;  // => undefined (although w is defined)
 y = x;  // => ReferenceError (because y was not defined)
 w = (var z=[x,y,3]).length; // SyntaxError (because unexpected token "var" next to z) (also, if it had worked the code inside the parenthesis would have returned undefined, of which undefined.length is a TypeError)
 return w;
};

At any rate, because our

let q

couldn't be integrated into our one-liner, we have to bring back the curly braces (

{...}

) and

return

statement, since we can't return our

value implicitly.

//Remember that this form, known as FUNCTIONAL FORM,...
var f = x => x;
// Means the same as this form, known as FUNCTIONAL-IMPERATIVE FORM,...
var f = x => { return x; }
// Means the same as this form known as IMPERATIVE FORM
var f = function(x){ return x; }

So here is the new

qs()()

in detail.

/* @func: qs
 * @desc: querySelector[All] in one function
 * @param parent : (@default is document) A string or Element to find the query element(s)
 * @param query  : (required) A CSS string matching an id, class, or attribute of elements inside the parent.
 * @returns:
 *  null if nothing is found.
 *  Node if query matches one result.
 *  NodeList query matches more than one result.
 */
var qs = function(parent){
  return function(query){
    let q;	// q is declared in the inner function
    if(typeof(parent) === "string"){
      let parent_query = qs()(parent);
      return qs(parent_query)(query);
    } else {
      // If parent is undefined, use document.
      var parent_element = parent || document;
      q = parent_element.querySelectorAll(query);
      if(q.length > 1){
        // if q match more than one instance return all matches as a NodeList.
        return q;	  
      } else {
        // Otherwise, return the first element only
        // Note: If [] is returned, and [][0] is undefined (meaning no matches), return null.
        return (q[0]||null);
      }
    }
  } // inner function
} // outer function

Before I talk about what makes this different from the old version, I want to talk about two functions in the

Array

class. The

.find()

function matches the first instance of a query. The

.filter()

matches all instances of a query and returns an array. What if you use

.filter()

and it only returns one instance? You still have to tack on

[0]

to get that one item out of the returned array. The

.find()

function, is basically the

.filter()

function where that one item is returned without needed to append

[0]

if it finds something.

There is one other thing to note. If

.filter()

finds no results, it returns an empty array,

[]

, but

.find()

returns

undefined

. Furthermore, the zeroth item in an empty array,

[][0]

, is

undefined

The

.querySelector()

function is basically the

.find()

function for a

NodeList

, which makes

.querySelectorAll()

the

.filter()

function. But there is one problem:

.querySelector()

doesn't return

undefined

, it returns

null

, and

null

is not the same as

undefined

Just about all

.getElementsBy*()

function returns an empty array, like

.querySelectorAll()

. But

.getElementById()

returns

null

.querySelector()

. We still need

null

any way because

typeof([]) === "object"

and

typeof(null) === "object"

too. So if

q[0]

undefined

null

will be returned.

With that, we eliminate the all
variable that was in the old version of

qs()()

. While this function doesn't take advantage of template strings like the old version did, it finally eliminates

.querySelector()

, meaning

.querySelectorAll()

is the ultimate query function and the only one we need.

So that's the new

qs()()

. Eventually, I'd like to present a new library I'm working on called haqs which is a JavaScript library which has an emphasis on closures and functional programming.

Here at Hackernoon, I plan on describing the more simplified versions of some of these function. The haqs library version is a bit more complicated because I was a bit braggadocio with demonstrating the functional programming aspects. I would really like to see just an itty-bit of object-oriented programming to reduce the amount of repetition and static structuring.

I also want to apply functional patterns to write code with a concise behavior. Haqs isn't quite ready yet, but I integrate some of the stuff I'm talking about here into it as I would like for it to be used in my Codepen work.

We'll see how it turns out. Until next time, keep hacking!