javascript multiple AND conditions in IF statement inside for loop javascript

Question

I feel stupid because I´m stuck with a basic. I have three set of classes that contains paragraphs and I want to change the background color of each one depending on day (with New Dat.getDay().

I dont know how to mix for loop and if statements for each set of classes correctly. I guess it´s something simple but I missing it!

function changecolor() {
  var d = new Date();
  var n = d.getDay();
  var weekda = document.getElementsByClassName('weekdays');
  var sat = document.getElementsByClassName('saturday');
  var dom = document.getElementsByClassName('sun-fer');
  for (var i = 0; i < weekda.length && i < sat.length && i < dom.length; i++)
    if (n > 0 || n < 6) {
      weekda[i].setAttribute("style", "background-color:#0091ea;color:white;");
    }
  else if (n == 6) {
    sat[i].setAttribute("style", "background-color:#0091ea;color:white;");
  } else {
    dom[i].setAttribute("style", "background-color:#0091ea;color:white;");
  }
}
}
changecolor();

seems n > 0 || n < 6 should be n > 0 && n < 6 ... because every number is either greater than zero OR less than 6 (|| is OR, && is AND) — Jaromanda X
– Jaromanda X, Commented Jun 27, 2017 at 3:26

Dinesh undefined · Accepted Answer · 2017-06-27 03:27:28Z

2

You need to group conditions. Read more about Operator precedence

 for (var i = 0;( (i < weekda.length) && (i < sat.length) && (i < dom.length)); i++){
   // your code

 }

answered Jun 27, 2017 at 3:27

Dinesh undefined

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2 Comments

nnnnnn Over a year ago

But...< already has higher precedence than &&, so what does adding parentheses change?

Rounin Over a year ago

Good question. Is the answer that the parentheses make it easier for the human reader to visually parse the multiple condition (?)

Tigger · Accepted Answer · 2017-06-27 03:38:07Z

Part of the problem may be you have background-color:#0091ea;color:white; for all three options. Therefore you may not be seeing any change.

Personally I would break this up a little to make it more flexible and a little easier to read (and maintain). For example:

function changecolor() {
    var d = new Date();
    var e = null;
    var s = null;
    switch(d.getDay()) {
        case 6:
            e = document.getElementsByClassName('saturday');
            s = "background-color:#0091ea;color:white;";
            break;
        case 0:
            e = document.getElementsByClassName('sun-fer');
            s = "background-color:#0091ea;color:green;";
            break;
        default:
            e = document.getElementsByClassName('weekdays');
            s = "background-color:#0091ea;color:blue;";
    }
    // now update the color
    updateItem(e,s);
}

function updateItem(e,s) {
    var i, max = e.length;
    for(i=0;i<max;i++) {
        e[i].setAttribute("style",s);
    }
}

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