Develop Reference

Get text between 2 or more substrings

This is my first question, so excuse me if I mess something up. I'm new.
Anywho, recently I've been designing a function which takes a string and 2 substrings, and then returns an array of the positions of both substrings so I can later substring the actual string using the positions of the substrings I'm searching for. I hope that makes sense.
function m(s,s1,s2,prevTable){
var a = prevTable || []
if (s.indexOf(s1) > -1 && s.indexOf(s2, s.indexOf(s1)) > -1){
a.push([s.indexOf(s1),s.indexOf(s2, s.indexOf(s1))+s2.length])
s=s.substring(s.indexOf(s2, s.indexOf(s1)+s2.length))
console.log(s)
m(s,s1,s2,a);
}
return a;
}
So to summarize it makes an array (a), finds the position of s1 and s2 (plus it's own length so it includes s2) in the source string (s), adds them to the array as it's own array.
E.g a would be: a=[[2,5]], deletes up to where s2 was found (+s2.length to include s2), and then repeats it with the new string unless it can't find both s1 and s2, in which case it returns a.
However, it does not work as I intended it to.
Upon running this:
var s = "Hey. This is pointless. Middle is always neutral. This is not
pointless."
var a=m(s,"This","pointless.")
for (i=0;i<a.length;i++){
console.log(s.substring(a[i][0],a[i][1]))
}
The result I get is:
This is pointless.
dle is always neutral.
When I am expecting:
This is pointless.
This is not pointless.
Also, is there a name for this technique?

What you are trying to do could be accomplished more easily using regular expressions (MSDN Docs).
Here is a simple example, note: I threw this together quickly, it may not handle all input perfectly.
function splitBetweenTwoStrings(str, s1, s2){
var reg = new RegExp("("+s1+".*?"+s2+")", "g");
var result = [];
var r = null;
//get all instances and push into result array
while((r=reg.exec(str))){
result.push(r[1]);
}
return result;
}
console.log(splitBetweenTwoStrings("Hey. This is pointless. Middle is always neutral. This is not pointless.","This","pointless."))

You could do it by creating another method to check indices (I received help from (here)[https://stackoverflow.com/a/20968478/7535444]) and then loop over the occurrences.
var s = "Hey. This is pointless. Middle is always neutral. This is not pointless.";
var results = m(s, "This", "pointless.");
for (var i = 0; i < results.length; i++) {
console.log(results[i]);
}
function m(s, s1, s2) {
var s1Occurences = occurences(s, s1);
var s2Occurences = occurences(s, s2);
var loopCount = Math.min(s1Occurences.length, s2Occurences.length);
var results = [];
for (var i = 0; i < loopCount; i++) {
results.push(s.substring(s1Occurences[i], s2Occurences[i] + s2.length));
}
return results;
}
function occurences(main, sub) {
var indices = [];
for(var pos = main.indexOf(sub); pos !== -1; pos = s.indexOf(sub, pos + 1)) {
indices.push(pos);
}
return indices;
}

The problem with your code is, that in your example the second array element of "a" ([[5,23],[27,49]]) is relative to the temporary "s"-string created for the second call of m(). You would have to shift the values by the length of the cut-off-part of the "s"-string: [[5,23],[27+23,49+23]].
But I would recommend to use something like Will P.'s method.

Populate a prompt with elements of an array and number them off

(Stack Overflow doesn't have a tag for 'prompt' so I have used alert as I am guessing it is similar enough to attract the right answerers.)
Hello,
I am currently making a JavaScript-based game for an assignment at university. I am usually pretty good with problem solving but have been stumped by this issue.
To explain, I have an array which names the possible armour slots the player can pick. In any order these can be picked, and each time the choice gets pushed to a second array which handles what has already been picked (and in what order) and that item gets spliced from the original array. There is a while loop which runs through until all 3 have been picked.
var armourSlotToPick = ["Head", "Chest", "Legs"],
armourSlotPicked = [],
armourLoop = 1,
indexArmour = 0;
function numInArray() {
indexArmour++;
return (indexArmour + ". " + armourSlotToPick[indexArmour - 1] + "\n");
}
function armour() {
while (armourLoop < 4) {
var armourPick = prompt("Pick an armour slot to generate an item for:\n" + armourSlotToPick.forEach(numInArray));
if (armourPick == 1) {
armourSlotPicked.push(armourSlotToPick[0]);
armourSlotToPick.splice(0,1);
} else if (armourPick == 2) {
armourSlotPicked.push(armourSlotToPick[1]);
armourSlotToPick.splice(1,1);
} else if (armourPick == 3) {
armourSlotPicked.push(armourSlotToPick[2]);
armourSlotToPick.splice(2,1);
} else {
alert("Invalid choice, you suck");
break;
}
armourLoop++;
}
}
I know it probably wouldn't be possible to do the whole return in numInArray() to the prompt, but it shows some working.
Now the problem: I got it working so that each item in the array was numbered (var armourSlotToPick = ["1. Head", "2. Chest", "3. Legs"],) but as you could see, if the player chose 2, then the next time it would show "1. Head (new line) 3. Legs" and when the player chooses 3, a problem would occur, as they were really meant to choose 2. How is it possible to number the items in the array, in a prompt?
I'm possibly over thinking this but I have suffered for a few hours now.
I thank you in advance for any insight you may have,
Daniel.
EDIT: Solved.
Below is the end result, a slight variation from the edited answer from Jonathan Brooks.
var armourSlotToPick = [null, "Head", "Chest", "Legs"]
var armourSlotPicked = [null];
var armourLoop = 1;
function armour() {
while (armourLoop < 4) {
var message = "Pick an armour slot to generate an item for:\n";
for (var i = 0; i < armourSlotToPick.length; i++) {
if (armourSlotToPick[i] !== null) {
message += "" + i + ". " + armourSlotToPick[i] + "\n";
}
}
var armourPick = prompt(message);
if (armourPick > armourSlotToPick.length-1 || armourPick < 1) {
alert("Invalid choice, you suck");
} else {
var insert = armourSlotToPick.splice(armourPick, 1);
armourSlotPicked.push(insert);
}
armourLoop++;
}
armourSlotPicked.splice(0,1);
}
armour();
alert(armourSlotPicked.join("\n"));
I thank all that have contributed to this discussion and the end result, and I hope this is a good example for future problems people may have similar to this.

Check out my fiddle, I think I have a working solution.
What you really want to be using are Object Literals with your own indexing (starting from 1) - if it were me, I would create my own way to iterate over this custom indexing by adding a method to the Object's prototype, but I digress.
You're overcomplicating your code by using a while loop, and that large bulk of if statements is unnecessary: instead, all you need is some basic validation on the input and then you can just trust whatever input passes this validation. That is demonstrated here:
if ( armourPick > armourSlotToPick.length || armourPick < 1 ) {
alert("Invalid choice, you suck");
}
else {
armourSlotPicked.push( armourSlotToPick[armourPick-1] )
alert (armourSlotPicked[armourSlotPicked.length-1].value);
}
Read my code carefully, and you should get a better understanding of how to deal with certain issues.
EDIT:
As per your request, I think I have a solution that suits your needs. Basically all you have to do to have the arrays "start" at an index of 1 is to fill the zeroth element with a null value, like so:
var armourSlotToPick = [null, "Head", "Chest", "Legs"]
var armourSlotPicked = [null];
You just have to remember to take this null object into account in your code, for example:
if (armourSlotToPick[i] !== null) {
message += "" + i + "\n";
}
The indices will update automatically. See this updated fiddle for more details.

use structures / objects as content in the array, instead of just values.
the basic concept:
armourSlotPicked.push({ "key": 1, "value":armourSlotToPick[1]})
alert("value: " + armourSlotPicked[0].value)
alert("key: " + armourSlotPicked[0].key)
edit: responding to comments can take some space.
IMHO a prompt is the completely wrong tool for this, since most browsers would ask the user permission to prevent multiple popups, and since a promt can only return 1 piece of information, you can only ask for 1 thing per popup. Instead you ought to use a div element, with checkboxes for each information..
That being said it can easily be used in a promt.
The prompt is just a built in function, that takes a string as an argument (which is shown as text in the popup) and returns a string with the users input.
what does the magic for you is in fact this:
array.foreach(): The forEach() method executes a provided function once per array element.
in your case that means it calls a function that returns a string for each element in the array, and concatenates the strings.
in the old days you would have written this:
var messageText= "Pick an armour slot to generate an item for:\n"
for(var i = 1; i < armourSlotToPick.length; i++){
messageText += i + ". " + armourSlotToPick[i- 1] + "\n";
}
var armourPick = prompt(messageText);
but in this modern age, you define a printing function, and use it to generate the loop:
function numInArray() {
indexArmour++;
return (indexArmour + ". " + armourSlotToPick[indexArmour - 1] + "\n");
}
//more code before we get to where the function is used....
indexArmour = 0;
var messageText = "Pick an armour slot to generate an item for:\n" + armourSlotToPick.forEach(numInArray);
var armourPick = prompt(messageText);
or in a single line as in your code:
indexArmour = 0; //you forgot this - otherwise the list will only be complete once?
var armourPick = prompt("Pick an armour slot to generate an item for:\n" + armourSlotToPick.forEach(numInArray));
It produces the same output, because it does the same thing, its just written very differently!
If the array holds "object literals" instead of simply values, as I suggest, the old fashioned code would look something like this:
function contains(a, value) {
try{
for (var i = 0; i < a.length; i++) {
if (a[i].value == value) {
return true;
}
}
}
catch(err) {
// do nothing
};
return false;
}
and later..
for(var j = 0; j < 4; j++){
for(var i = 0; i < Math.min(armourSlotToPick.length); i++){
if( contains(armourSlotPicked, armourSlotToPick[i- 1]) )
continue;
var messageText = "Generate an item for armour in slot: " + i + "\n"
messageText += armourSlotToPick[i- 1] + "\n";
}
var armourPick = prompt(messageText);
if (armourPick > 0 && armourPick < armourSlotToPick.length) {
armourSlotPicked.push({"key":j, "value":armourSlotToPick[armourPick]);
}
...
}
//now we have an array that holds information about when what was picked..
or something along those lines.. this is bt.w completely untested, it's just for illustration

You want to use the array index to number your items. Since your numbers are one-based and the index is zero-based, you will need to convert between the two when outputting and interpreting the response.
This approach will also allow you to eliminate all but two of the cases in your if-else statement.

Skipping multiple elements in a FOR loop, Javascript

I have some file contents I'd like to pass on to my server using a javascript function. In the file, there are many empty lines, or those which contain useless text. So far I read every line in as a string stored in an array.
How do I then loop through that content skipping multiple lines such as lines 24,25, 36, 42, 125 etc. Can I put these element id's into an array and tell my for loop to run on every element except these?
Thanks

you can't tell your for loop to iterate all, but skip certain elements. it will basically just count in any direction (simplified) until a certain critera has been met.
you can however put an if inside your loop to check for certain conditions, and chose to do nothing, if the condition is met. e.g.:
(pseudo code below, beware of typing errors)
for(var line=0; line < fileContents.length; line++) {
if(isUselessLine(line)) {
continue;
}
// process that line
}
the continue keyword basically tells the for loop to "jump over" the rest of the current iteration and continue with the next value.
The isUselessLine function is something you'll have to implement yourself, in a way, that it returns true, if the line with the given linenumber is useless for you.

You can try this its not much elegent but will suerly do the trick
<html>
<body>
<p>A loop which will skip the step where i = 3,4,6,9.</p>
<p id="demo"></p>
<script>
var text = "";
var num = [3,4,6,9];
var i;
for (i = 0; i < 10; i++) {
var a = num.indexOf(i);
if (a>=0) {
continue;
}
text += "The number is " + i + "<br>";
}
document.getElementById("demo").innerHTML = text;
</script>
</body>

You could use something like this
var i = 0, len = array1.length;
for (; i < len; i++) {
if (i == 24 || i == 25) {
array1.splice(i, 1);
}
}
Or you can have an another array variable which got all the items that need to be removed from array1

Another method:
var lines = fileContents.match(/[^\r\n]+/g).filter(function(str,index,arr){
return !(str=="") && uselessLines.indexOf(index+1)<0;
});

If you have many indices to skip, and this depends on the elements of the array, you could write a function that returns the number of elements to skip over for each index in that array (or returns 1, if no skipping required):
for ( let i = 0;
i < array.length;
i += calcNumberOfIndicesToSkip( array, i )){
// do stuff to the elements that aren't
// automatically skipped
}
function calcNumberOfIndicesToSkip( array, i ){
// logic to determine number of elements to skip
// (this may be irregular)
return numberOfElementsToSkip ;
}
In your case:
// skip the next index (i+1)?
for ( let i=0; i<array.length; i+=skipThisIndex(i+1) ){
// do stuff
}
function skipThisIndex(i){
const indicesToSkip = [ 24, 25, 36, 42, 125 ];
return 1 + indicesToSkip.includes(i);
}
// returns 1 if i is not within indicesToSkip
// (there will be no skipping)
// => (equivalent to i++; normal iteration)
// or returns 1 + true (ie: 2) if i is in indicesToSkip
// => (index will be skipped)

Recursively constructing a JavaScript array of all possible combinations while respecting order

I am having difficulty getting the following concept in to code:
Let's say we are given the following array:
[
'h1,h2',
'span,style'
]
From this I wish to get the following output:
[
'h1 span',
'h1 style',
'h2 span',
'h2 style
]
So that we have an array of strings containing all combinations of the original array, which also respects order (so span h1 and style h2 are not valid).
To describe verbose: I have a single level array of strings which are effectively comma separated values. I wish to iterate over this array and split these strings by their comma in to a new array, and for each index in this new array build a new string which contains all the other split values from subsequent indexes in the original array.
I am having difficulty trying to program this in JavaScript. I understand that I will need some recursion, but I'm confused about how to do it. After trying various different and failing methods, I currently have this:
function mergeTagSegments(arr, i, s) {
i = i || 0;
s = s || '';
if(!arr[i]) { return s; }
var spl = arr[i].split(',');
for(var j in spl) {
s += spl[j] + mergeTagSegments(arr, i+1, s);
}
return s;
}
This also fails to work as intended.
I feel a little embarrassed that I am unable to complete what I originally thought was such a simple task. But I really hope to learn from this.
Many thanks in advance for your advice and tips.

Your thinking along the right lines. Recursion is definetly the way to go. I have implemented a suggested solution below, which should give you the desired output.
var values = ['h1,h2', 'span,style'];
function merge(input, index) {
var nextIndex = index + 1;
var outputArray = [];
var currentArray = [];
if(index < input.length) {
currentArray = input[index].split(',');
}
for(var i = 0, end = currentArray.length; i < end; i++) {
if(nextIndex < input.length) {
merge(input, nextIndex).forEach(function(item) {
outputArray.push(currentArray[i] + ' ' + item);
});
}
else {
outputArray.push(currentArray[i]);
}
}
return outputArray;
}
var output = merge(values, 0, '');
console.log(output);

Can anyone see what is wrong with my Javascript?

I have written the following:
var pages=["[www.google.co.uk] This is the WWW. ","[www.yahoo.co.uk] This is also the WWW. "];
function findScoresC(s){
var scores=[];
var words=[];
var wordScore;
var indexScore=[];
s=s.toLowerCase();
for(i=0;i<pages.length; i++){
var lowerCaseContents=(pages[i].substring(pages[i].indexOf("]")+1,pages[i].lastIndexOf(" "))).toLowerCase();
words=lowerCaseContents.split(" ");
for(i=0;i<words.length;i++){
if(words[i].match(s)){
wordScore=1;
indexScore[i]=indexScore[i]+1};
scores[i] =indexScore[i]}};
return scores;
}
alert(findScoresC("w"));
The function aims to return an array ("scores") where each index of the array is the number of times the string s is found in each index of the "pages" array, excluding what is inside the square brackets - however, only finding the string s once within each word. So ideally, the first index of scores would be 1, because I have called the function with the letter w, and i would only like it to find the first w of "WWW" in the first index of pages - if this makes sense.
I have confused myself pretty epically in getting this far, so I have no idea why the function is returning ",,,," rather than numerical values for each index of scores - any ideas?
Thanks

When your for loop exits, i is equal to words.length, which is one greater than the last index of indexScore. You are assigning nothing at all to scores[i] each time through.

It might be because you have a nested for loop with the same index variable.

var pages=["[www.google.co.uk] This is the WWW. ","[www.yahoo.co.uk] This is also the WWW. ";
function findScoresC(s){
var scores=[];
var words=[];
s=s.toLowerCase();
for(i=0;i<pages.length; i++)
{
scores[i]=0;
var lowerCaseContents=(pages[i].substring(pages[i].indexOf("]")+1,pages[i].lastIndexOf(" "))).toLowerCase();
words=lowerCaseContents.split(" ");
for(j=0;j<words.length;j++)
{
if(words[j].match(s))
{
scores[i] += 1;
}
}
}
return scores;
}
alert(findScoresC("w"));
There were a few things. I replaced "i" with "j" for the inner index. You don't require a semicolon after a closing paren. You should have a semicolon after instructions (a couple were missing).
Probably the main issue (after the "i" issue) was that scores[i] should have been set outside the inner loop. This would have been clearer if the cosing parens had been separated out onto separate lines, instead of like "scores[i] =indexScore[i]}};".
It turned out that the variable indexScore was not required. That allowed me to bring scores[i] inside the inner loop to accumulate word hits directly.
Finally, I would prefer to communicate the pages variable to the function as an argument than to assume that it is available in the global space. I tend to avoid globals if I can.
var pages = [...];
function findScoresC(pages, s)
{
...
}
alert(findScoresC(pages, "w"));

Here's you're function fixed. It returns [1,1] which appears to be what you were going for. My notes are in the code.
var pages=["[www.google.co.uk] This is the WWW. ","[www.yahoo.co.uk] This is also the WWW. "];
function findScoresC(s){
var scores = [],
words = [],
wordScore;
// indexScore = [] <- this doesn't seem necessary
s = s.toLowerCase();
// Make sure to use `var i` and not just `i`; otherwise, you are creating a global variable.
for ( var i=0; i<pages.length; i++ ) {
// Initialize me!
scores.push(0);
var lowerCaseContents = pages[i].substring(
pages[i].indexOf("]") + 1, pages[i].lastIndexOf(" ")
).toLowerCase();
words = lowerCaseContents.split(" ");
// You were using `i` for this loop as well. No can do.
for ( var j=0; j<words.length; j++) {
if ( words[j].match(s) ) {
// wordScore = 1; <- I don't know what you're using this for
scores[i]++;
}
}
};
return scores;
}
console.log(findScoresC("w"));

here's a small function that counts how many times substring "subStr" occurs in "str", not counting [...]
function substrCount(str, subStr) {
var str = str.replace(/\[.+?\]/g, "");
var del = str.toLowerCase().split(subStr.toLowerCase()).join("");
return (str.length - del.length) / subStr.length;
}
the rest is obvious ;)
// edit: this is how you apply this function to an array
var someArray = ["whatever", "something", "else" ];
var counter = [];
for(var i = 0; i < someArray; i++)
counter[i] = substrCount(someArray[i], "something");
// or, to count only one match, i.e. just to test if a substring is present
counter[i] = substrCount(someArray[i], "something") > 0;