Should I add the unit 'px' to numerical values in the css function of jQuery?

Question

Is there any difference between the following?

$(elem).css({ height : 100 })

$(elem).css({ height : 100+'px' })

I've been searching for a long time in Google and I haven't found the answer. On jquery.com there are examples with px and just integer values... Is there some difference in browsers or OS ?

Answer 1

jQuery automatically adds the unit 'px' (as a default unit) to all numbers for the most css properties, including "height":

See line 221 in src/css.js

// If a number was passed in, add 'px' to the (except for certain CSS properties)
if ( type === "number" && !jQuery.cssNumber[ origName ] ) {
    value += "px";
}

!jQuery.cssNumber[ origName ] excludes the following css properties:

• columnCount
• fillOpacity
• fontWeight
• lineHeight
• opacity
• orphans
• widows
• zIndex
• zoom

(Side note: If you are like me at first a bit surprised about the exclusion of "lineHeight": a number without a unit will be multiplied with the current font size to set the line height - so there is a difference for the property 'line-height' when you specify / omit the unit)