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custom querySelectorAll implemention

This was given to me as an interview question -- didn't get the job, but I still want to figure it out.
The objective is to write two querySelectorAll functions: one called qsa1 which works for selectors consisting of a single tag name (e.g. div or span) and another called qsa2 which accepts arbitrarily nested tag selectors (such as p span or ol li code).
I got the first one easily enough, but the second one is a bit trickier.
I suspect that, in order to handle a variable number of selectors, the proper solution might be recursive, but I figured I'd try to get something working that is iterative first. Here's what I've got so far:
qsa2 = function(node, selector) {
var selectors = selector.split(" ");
var matches;
var children;
var child;
var parents = node.getElementsByTagName(selectors[0]);
if (parents.length > 0) {
for (var i = 0; i < parents.length; i++) {
children = parents[i].getElementsByTagName(selectors[1]);
if (children.length > 0) {
for (var i = 0; i < parents.length; i++) {
child = children[i];
matches.push(child); // somehow store our result here
}
}
}
}
return matches;
}
The first problem with my code, aside from the fact that it doesn't work, is that it only handles two selectors (but it should be able to clear the first, second, and fourth cases).
The second problem is that I'm having trouble returning the correct result. I know that, just as in qsa1, I should be returning the same result as I'd get by calling the getElementsByTagName() function which "returns a live NodeList of elements with the given tag name". Creating an array and pushing or appending the Nodes to it isn't cutting it.
How do I compose the proper return result?
(For context, the full body of code can be found here)

Here's how I'd do it
function qsa2(selector) {
var next = document;
selector.split(/\s+/g).forEach(function(sel) {
var arr = [];
(Array.isArray(next) ? next : [next]).forEach(function(el) {
arr = arr.concat( [].slice.call(el.getElementsByTagName(sel) ));
});
next = arr;
});
return next;
}
Assume we always start with the document as context, then split the selector on spaces, like you're already doing, and iterate over the tagnames.
On each iteration, just overwrite the outer next variable, and run the loop again.
I've used an array and concat to store the results in the loop.
This is somewhat similar to the code in the question, but it should be noted that you never create an array, in fact the matches variable is undefined, and can't be pushed to.

You have syntax errors here:
if (parents.length > 0) {
for (var i = 0; i < parents.length; i++) {
children = parents[i].getElementsByTagName(selectors[1]);
if (children.length > 0) {
for (var i = 0; i < parents.length; i++) { // <-----------------------
Instead of going over the length of the children, you go over the length of the parent.
As well as the fact that you are reusing iteration variable names! This means the i that's mapped to the length of the parent is overwritten in the child loop!
On a side note, a for loop won't iterate over the elements if it's empty anyway, so your checks are redundant.
It should be the following:
for (var i = 0; i < parents.length; i++) {
children = parents[i].getElementsByTagName(selectors[1]);
for (var k = 0; k < children.length; i++) {
Instead of using an iterative solution, I would suggest using a recursive solution like the following:
var matches = [];
function recursivelySelectChildren(selectors, nodes){
if (selectors.length != 0){
for (var i = 0; i < nodes.length; i++){
recursivelySelectChildren(nodes[i].getElementsByTagName(selectors[0]), selectors.slice(1))
}
} else {
matches.push(nodes);
}
}
function qsa(selector, node){
node = node || document;
recursivelySelectChildren(selector.split(" "), [node]);
return matches;
}

How can I skip a specific Index in an array in a for loop javascript

Suppose I had a function that is pulling in values from somewhere and storing those values into an array.
function getSport(ply) {
some code here... //function gets values that I need for array later
}
var sports1 = getSport(playerChoice);
var sports2 = getSport(playerChoice);
var sports3 = getSport(playerChoice);
var sports4 = getSport(playerChoice);
var sportsArry = [sports1, sports2, sports3, sports4];
Now I would like to use a for loop to loop the elements, the problem, however, is the first index (index 0) will always be true. I want to skip index 0. How do I do that? Further I want to replace index 0 with something else. Let me show you
for (var i = 0; i<sportsArry.length; i++){
if ( (sports1 == sportsArry[i]) ) {
sports1 = null; //I figured I should null it first?
sports1 = replaceValueFunc(playerChoice2);
}
}
Well you can see the problem I would have. Index 0 is true.
Let me show you what would work, although it requires alot of or operators.
if ( (sports1 == sportsArry[1]) || (sports1 == sportsArry[2]) || (sports1 == sportsArry[3] ) {
...
}
^^ That is one way to skip index 0, what would be another better looking way?

I want to skip index 0. How do I do that? Further I want to replace
index 0 with something else.
Just start the loop from 1 instead of 0
sportsArr[0] = "Something else"; // set the first element to something else
for(var i = 1; i < sportsArr.length; i++){
// do something
}

Loop through array checking for indexOf's more simple?

Okay, like the title says. I have a array looking like this:
var hiTriggers = new Array();
hiTriggers = ["hi", "hai", "hello"];
And I'd like to check through it if it finds either of those. I can already achieve this by doing the following:
if(message.indexOf("hi") >= 0) {
// do whatever here!
}
But I'm looking for an more efficient way rather than doing 100 if() checks. Such as loop through an array with the "hiTriggers".
I tried the following:
for(var i; i < hiTriggers.length; i++) {
console.log(hiTriggers[i]); // simply to know if it checked them through)
if(message.indexOf(hiTriggers[i]) >= 0) {
//do stuff here
}
}
Which sadly did not work as I wanted as it does not check at all.
Thanks in advance and I hope I made sense with my post!
Edit; please note that I have 'messaged' already 'declared' at another place.

It doesn't run because you didn't give the i variable an initial value. It is undefined.
Change to use var i=0;:
for(var i=0; i < hiTriggers.length; i++) {
//console.log(hiTriggers[i]); // simply to know if it checked them through)
if(message.indexOf(hiTriggers[i]) >= 0) {
//do stuff here
console.log("found " + hiTriggers[i]);
}
}

Try using a regular expression to match the message. The \b is a word boundary marker, and the words between the | characters are what is being searched for. If any of the words appear in the message, then message.match will return the array of matches, otherwise null.
var pattern = /\b(Hello|Hi|Hiya)\b/i;
var message = "Hello World";
if (message.match(pattern))
{
console.log("do stuff");
}

You can write even simpler using a for in loop:
for(var v in hiTriggers){
if(message.indexOf(hiTriggers[v]) >= 0) {
//do stuff here
console.log("found " + hiTriggers[v]);
}
}

Problem is becoz - you have not initialized your var i, make it var i = 0;
You can try forEach loop.
hiTriggers.forEach(function(e) {
if(message.indexOf(e) >= 0) {
//do sthg here
}
})

Better solution to find a cell in an array

I have the following array:
var myArray = [
{
"id":1,
"name":"name1",
"resource_uri":"/api/v1/product/1"
},
{
"id":5,
"name":"name2",
"resource_uri":"/api/v1/product/5"
}
]
Each row is identified by it's unique id. I am quite new to Javascript and was wondering what was the best solution to find a cell based on id.
For example, for the id:5; my function must return:
findCell(myTable, id=5);
// this function must return:
{
"id":5,
"name":"name2",
"resource_uri":"/api/v1/product/5"
}
I'm quite afraid to do an ugly for loop... Maybe there is some built-in javascript function to perform such basic operations.
Thanks.

Yes there is a built-in function - filter. I would use it like this:
findCells(table, property, value) {
return table.filter(function (item) {
return item[property] === value;
});
}
findCells(myTable, "id", 5);
This is a bit modified version, of what you want: it can find all cells by the specified property name value.
Edit: using for loop to search the first occurence of the element is okay, actually:
findCell(table, id) {
var result = null;
for (var i = 0, cell = table[0], l = table.length; i < l; i++, cell = table[i]) {
if (cell.id === id) {
result = cell;
break;
}
}
return result;
}
findCell(myTable, 5);

Try this expression this might be helpful
var result = myArray.filter(function(element, index) { return element.ID == 5; });
filter() has two parameters
element - current row
index - current row index.

If you are going to stick with the array, the 'ugly' for loop is your best bet for compatibility. It's not that ugly when put in a function:
function findById(id) {
for(var i = 0; i < myArray.length; ++i) {
if(myArray[i].id === id) return myArray[i];
}
}
// Not checking return value here!
alert(findById(5).name);
Filter is another option if your concern is only with recent versions of browsers. It will return an array of values.
If your array is very large though, it would make sense to introduce some sort of index for efficient lookups. It adds an additional maintenance burden, but can increase performance for frequent lookups:
var index = {};
for(var i = 0; i < myArray.length; ++i) {
index[myArray[i].id] = i;
}
// Find element with id=5
alert(myArray[index[5]].name);
Example

Check if an HTML element with the same id exists

Can this be done using javascript?

If you're trying to find out if more than one element share one id, with jQuery you could do $('[id=blah]').length - that will return a count of all elements where the id is equal to 'blah'. See the fiddle. If it's greater than 1 then you have a duplicate id.
Edit: I've tested this in Chrome, FF and IE6, and all of them show that there are two elements with the same id. I agree that it's really bad form to have more than one element share an id, but this code does work.

Maybe (if I understand the question)
if (document.getElementById('theId')) {
}

Also, in order to print all duplicates:
var elems = document.getElementsByTagName('*');
var num = elems.length;
var ids = [ ];
for(i=0; i<num; i++ ) {
var id = elems[i].getAttribute('id');
if(id != null) {
if(ids.indexOf(id) >=0 ) {
console.debug(id); // found in table
} else {
ids.push(id); // new id found, add it to array
}
}
}

if(!document.getElementById('search')) { return; }

Yes it is.
iterate thru document.getElementsByTagName('*'), use element.getAttribute('id')