How can I select the last 4 characters of a string using JavaScript?

Question

This code chooses the highest numerical value between the data ids and adds an lime background to it. btw these numbers are hex values. my problem is that in hex values its the matter of the last 4 values but my code takes the whole characters. how can i make my code work for only the last 4 characters?

Im sorry this might be easy to solve for you but i tried over and over again and couldnt make it work.

Hex to decimal:

dc61 = 56417

dc62 = 56418

dc63 = 56419

dc64 = 56420

 maxData = $(".answers li[data-id]").get ().reduce  ( (maxObj, crrntNode) => {
 
    var idVal   = parseInt ( $(crrntNode).data("id"), 16) ; 

    if (idVal > maxObj.value) {
        maxObj.value  = idVal;
        maxObj.node   = crrntNode;
    }
    return maxObj;
  },
  {value: 0, node: null}
);
$("body").append (`<p>The highest data-id value was ${maxData.value}.</p>`)
$(maxData.node).css ("background", "lime");

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="question-text" class="question sp-element border-radius active">What is favorite colour?</div>
          <ul class="answers" id="answers">
            <li data-id="58b9890062279282090ddc61" class="answer sp-element border-radius active">Purple</li>
            <li data-id="58b9890062279282090ddc63" class="answer sp-element border-radius active">Blue</li>
            <li data-id="58b9890062279282090ddc64" class="answer sp-element border-radius active">Yellow</li>
            <li data-id="58b9890062279282090ddc62" class="answer sp-element border-radius active">Red</li>
          </ul>

Is the desired result different than what this previous SO answer provides? https://stackoverflow.com/questions/5873810/how-can-i-get-last-characters-of-a-string-using-javascript — pastaleg, Dec 20 '17 at 21:37

score 9 · Answer 1 · answered Dec 20 '17 at 21:38

9

If I understand your question correctly (and I'm not sure I do), you just want to take the last 4 characters of a known string (to translate into decimal, but that wasn't your question).

In javascript, you would want to use the substring api. For example, to get the last 4 digits of an arbitrary string, you could do this:

var str = "abcdefghijklmnop";
var substr = str.substring(str.length-4, str.length);

More information: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/substring

answered Dec 20 '17 at 21:38

Eric

433
5
12

How is this answer any different than mine? – Scott Marcus Dec 20 '17 at 21:39
1

It's not. We both started posting when the question had no answers, I would guess. – Eric Dec 20 '17 at 21:40
Uh, no. My answer was posted 4 minutes before yours. – Scott Marcus Dec 20 '17 at 21:41
Thank u very much – Nur Bar Dec 20 '17 at 22:08
@ScottMarcus, yes, but you shouldn't have given that answer at all. Rather should've closed the question as a duplicate and/or tailored the answer to the OP's specifics, like Dryden Long did. You've got 20+K and a dupe hammer. Eric does not. – Brock Adams Dec 20 '17 at 23:11

score 3 · Answer 2 · answered Dec 20 '17 at 21:34

3

Use the String.substr(startPosition, numChars) method:

var myString = "abcdefg";
console.log(myString.substr(-4, 4)); // Start 4 chars before end and take 4 chars

answered Dec 20 '17 at 21:34

Scott Marcus

64,069
6
49
71

I tried this code before but i couldnt make it work on my coding :/ – Nur Bar Dec 20 '17 at 21:37
But, as you can see, this is the way and it works. What, in your code, contains the string that you need the last 4 chars of? – Scott Marcus Dec 20 '17 at 21:37
Thank u very much – Nur Bar Dec 20 '17 at 22:09

score 2 · Accepted Answer · answered Dec 20 '17 at 21:37

By using substr you can get the last 4 characters of the data attribute. So, instead of:

var idVal = parseInt($(crrntNode).data("id"), 16);

You can do something like this:

var nodeId = $(crrntNode).data("id");
var idVal = parseInt(nodeId.substr(nodeId.length - 4), 16);

 maxData = $(".answers li[data-id]").get ().reduce  ( (maxObj, crrntNode) => {
    var nodeId = $(crrntNode).data("id");
    var idVal = parseInt(nodeId.substr(nodeId.length - 4), 16); 

    if (idVal > maxObj.value) {
        maxObj.value  = idVal;
        maxObj.node   = crrntNode;
    }
    return maxObj;
  },
  {value: 0, node: null}
);
$("body").append (`<p>The highest data-id value was ${maxData.value}.</p>`)
$(maxData.node).css ("background", "lime");

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="question-text" class="question sp-element border-radius active">What is favorite colour?</div>
          <ul class="answers" id="answers">
            <li data-id="58b9890062279282090ddc61" class="answer sp-element border-radius active">Purple</li>
            <li data-id="58b9890062279282090ddc63" class="answer sp-element border-radius active">Blue</li>
            <li data-id="58b9890062279282090ddc64" class="answer sp-element border-radius active">Yellow</li>
            <li data-id="58b9890062279282090ddc62" class="answer sp-element border-radius active">Red</li>
          </ul>

Thank u so much i so my mistake , i will give u the green button in 8 minutes :) — Nur Bar, Dec 20 '17 at 21:41
I have another problem. when data-id was changing code selecting old values not research again on data ids. Do u have idea ? — Nur Bar, Dec 20 '17 at 22:17

How can I select the last 4 characters of a string using JavaScript?

3 Answers3