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Thread: 'filter' function modification

  1. #1
    Join Date
    Dec 2005
    Location
    TX
    Posts
    7,931

    Question 'filter' function modification

    I modified the following code from:
    https://www.w3schools.com/jsref/tryi...ryjsref_filter

    It works OK, but I would like to change it further.

    I wish to somehow pass the GLOBAL variable 'state'
    as part of the 'filter' function so as to avoid global assignments.

    How is the information passed in the 'filter' function?

    Code:
    <!DOCTYPE html>
    <html lang="en">
    <head>
    <meta charset="UTF-8" />
    <title> filter() test </title>
    <body>
    
    <pre>
     Count 'y' &amp; 'n' &amp '-' characters
     in this array ['y','n','y','n','y']
    </pre>
    <button onclick="myFunction()">Try it</button>
    <pre id="demo"></pre>
    
    <script>
      function doc(IDS) { return document.getElementById(IDS); }  // reduce typing function
    
      var consent = ['y','n','y','n','y'],
          state = 'y';
      function checkConsent(YN) { return YN == state; }
    
      function myFunction() {
        state = 'y';  doc("demo").innerHTML  = 'Y: '+ consent.filter(checkConsent).length+'<br>';
        state = 'n';  doc("demo").innerHTML += 'N: '+ consent.filter(checkConsent).length+'<br>';
        state = '-';  doc("demo").innerHTML += '-: '+ consent.filter(checkConsent).length+'<br>';
      }
    </script>
    </body>
    </html>
    Last edited by JMRKER; 01-08-2018 at 10:44 PM.

  2. #2
    Join Date
    Dec 2012
    Posts
    1,611
    Unfortunately the parameters of the callback function cannot be modified. The only solution I'm aware of is this:
    Code:
            function myFilter(arr, state) {
                function checkConsent(YN) {
                    return YN == state;
                }
                return arr.filter(checkConsent);
            }
            function myFunction() {
                doc("demo").innerHTML = 'Y: ' + myFilter(consent, 'y').length + '<br>';
                doc("demo").innerHTML += 'n: ' + myFilter(consent, 'n').length + '<br>';
                doc("demo").innerHTML += '-: ' + myFilter(consent, '-').length + '<br>';
            }
    Unfortunately defining the callback in the global scope doesn't work:
    Code:
            function checkConsent(YN) {
                return YN == state;
            }
            function myFilter(arr, state, callback) {
                return arr.filter(callback);
            }
            function myFunction1() {
                doc("demo").innerHTML = 'Y: ' + myFilter(consent, 'y', checkConsent).length + '<br>';
                doc("demo").innerHTML += 'n: ' + myFilter(consent, 'n', checkConsent).length + '<br>';
                doc("demo").innerHTML += '-: ' + myFilter(consent, '-', checkConsent).length + '<br>';
            }

  3. #3
    Join Date
    Dec 2012
    Posts
    1,611
    PS: Researched further and figured out this:
    Code:
            function checkConsent(YN) {
                return YN == this.state;
            }
            function myFilter(arr, st, callback) {
                var par = { state: st };
                return arr.filter(callback, par);
            }
            function myFunction1() {
                doc("demo").innerHTML = 'Y: ' + myFilter(consent, 'y', checkConsent).length + '<br>';
                doc("demo").innerHTML += 'n: ' + myFilter(consent, 'n', checkConsent).length + '<br>';
                doc("demo").innerHTML += '-: ' + myFilter(consent, '-', checkConsent).length + '<br>';
            }
    Explanation:
    [url]https://developer.mozilla.or
    Last edited by Sempervivum; 01-09-2018 at 05:30 AM.

  4. #4
    Join Date
    Dec 2012
    Posts
    1,611

  5. #5
    Join Date
    Dec 2012
    Posts
    1,611
    PPS: This procedure can be easily applied to your initial code:
    Code:
            function checkConsent(YN) {
                return YN == this.state;
            }
    
            function myFunction1() {
                doc("demo").innerHTML = 'Y: ' + consent.filter(checkConsent, {state: 'y'}).length + '<br>';
                doc("demo").innerHTML += 'n: ' + consent.filter(checkConsent, {state: 'n'}).length + '<br>';
                doc("demo").innerHTML += '-: ' + consent.filter(checkConsent, {state: '-'}).length + '<br>';
            }

  6. #6
    Join Date
    Dec 2005
    Location
    TX
    Posts
    7,931
    Quote Originally Posted by Sempervivum View Post
    PPS: This procedure can be easily applied to your initial code:
    Code:
            function checkConsent(YN) {
                return YN == this.state;
            }
    
            function myFunction1() {
                doc("demo").innerHTML = 'Y: ' + consent.filter(checkConsent, {state: 'y'}).length + '<br>';
                doc("demo").innerHTML += 'n: ' + consent.filter(checkConsent, {state: 'n'}).length + '<br>';
                doc("demo").innerHTML += '-: ' + consent.filter(checkConsent, {state: '-'}).length + '<br>';
            }
    Thank you for the code and the reference.
    Nice solution.

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