Add CSS attributes to element with JavaScript

Question

I want to add CSS attributes to my element, but my current solution loses all previous attributes that had an impact on the element.

function checkNr(id) {
  var value = document.getElementById(id).value;
  if (parseFloat(value) == NaN) {
    document.getElementById(id).setAttribute("style", "border:2px solid red; background-color: rgb(255, 125, 115);");
  }
  else {
    document.getElementById(id).setAttribute("style", "border:default; background-color: rgb(255, 255, 255);");
  }
}

Before using this method the element already had the attributes:

float: left;
width: 50px;

Afterwards, the element loses these attributes, leaving only the specific attributes from the JavaScript method. So, I want to add attributes without replacing them.

Answer 1

Setting the style attribute like that, overwrites the attribute and removes previously set styles.

What you really should do is set the styles directly instead by changing the style property :

function checkNr(id) {
    var elem  = document.getElementById(id),
        value = elem.value;
    if (parseFloat(value) == NaN) {
        elem.style.border = '2px solid red'; 
        elem.style.backgroundColor = 'rgb(255, 125, 115)';
    } else {
        elem.style.border = 'none'; 
        elem.style.backgroundColor = 'rgb(255, 255, 255)';
    }
}

Answer 2

function checkNr(id) {
    var elem = document.getElementById(id);
    var css = {};
    if (parseFloat(elem.value) == NaN) {
        css = { border: '2px solid red', backgroundColor: 'rgb(255, 125, 115)' };
    } else {
        css = { border: 'none', backgroundColor: 'rgb(255, 255, 255)' };
    }

    Object.assign(elem.style, css);
}

Answer 3

The simplest way for me is:

prev_style=obj.getAttribute("style");
added_style="background-color:red;"
if (prev_style==undefined || prev_style==null) { prev_style="" }
obj.setAttribute("style",prev_style+added_style);

or with jQuery

$(obj).attr("style",prev_style+added_style)

Answer 4

Setting the style attribute of the element directly will overwrite any previous value:

element.setAttribute("style", "border: 2px solid red; /* ... */")

<div id="element" style="float: right; /* ... */">...</div>
<!-- becomes -->
<div id="element" style="border:; 2px solid red; /* ... */">...</div>

Instead, set one property at a time using the element.style.property = value syntax:

const checkNr = id => {
  const element = document.getElementById(id)
  const isNotNum = isNaN(parseFloat(element.value))
  element.style.background = `rgb(255, ${isNotNum ? "125, 115" : "255, 255"})`
  element.style.border = isNotNum ? "2px solid red" : "default"
}

Or, even better, add a conditional CSS class:

const checkNr = id => {
  const element = document.getElementById(id)
  const isNotNum = isNaN(parseFloat(element.value))
  element.classList.add(isNotNum ? "not-number" : "is-number");
}

.not-number {
  background-color: rgb(255, 125, 115);
  border: 2px solid red;
}
.is-number {
  background-color: rgb(255, 255, 255);
  border: default;
}

Answer 5

jQuery option:

This will add a red border without removing any other inline styles:

jQuery('#element-id').css('border', '1px solid red');

Note: You need to add jQuery as a dependency to your project for this to work.

• jQuery website: https://jquery.com/
• css() documentation: https://api.jquery.com/css/