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How can i get default font size in pixels by using JavaScript or JQuery?

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Happy的楠姐
Happy的楠姐 2021-02-04 09:07

As you know em is a relative font measurement where one em is equal to the height of the letter \"M\" in the default font size. An advantage in using it is because you will be a

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  • 北海茫月
    2021-02-04 09:39

    There are a couple of situations this can be useful- 

    function getDefaultFontSize(pa){
 pa= pa || document.body;
 var who= document.createElement('div');

 who.style.cssText='display:inline-block; padding:0; line-height:1; position:absolute; visibility:hidden; font-size:1em';

 who.appendChild(document.createTextNode('M'));
 pa.appendChild(who);
 var fs= [who.offsetWidth, who.offsetHeight];
 pa.removeChild(who);
 return fs;
}

    alert(getDefaultFontSize())

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  • 春和景丽
    2021-02-04 09:42

    I believe the M-principle is a myth. At the very least the following documentation from http://www.w3.org/TR/CSS21/syndata.html proves that calculations based on the M-principle are overly complicated and unnecessary.

    The 'em' unit is equal to the computed value of the 'font-size' property of the element on which it is used. The exception is when 'em' occurs in the value of the 'font-size' property itself, in which case it refers to the font size of the parent element. It may be used for vertical or horizontal measurement. (This unit is also sometimes called the quad-width in typographic texts.)

    From this documentation the following are true.

    1. Without ancestor magnification, 1em is exactly equal to the pixel font size.

    2. Since ancestor magnification with ems and percent works in well defined ways a simple loop will calculate exact font sizes, assuming: no C.S.S; and some ancestor has it's font size set in absolute units.

    3. Since ems measure width you can always compute the exact pixel font size by creating a div that is 1000 ems long and dividing its client-Width property by 1000. I seem to recall ems are truncated to the nearest thousandth, so you need 1000 ems to avoid an erroneous truncation of the pixel result.

    4. You probably can create a font where the M-principle fails since em is based on the font-size attribute not on the actual font. Suppose you have a weird font where M is 1/3 the size of the other characters and you have a font size of 10 pixels. I kind of think the font-size is a guarantee of maximal character height and so the M will not be 10 pixels and all other characters 30 pixels.

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  • 無奈伤痛
    2021-02-04 09:42

    If you use rem as unit the default 'font-size' need take from <html>, not from body or other.

    alert(window.getComputedStyle(document.documentElement).getPropertyValue('font-size'))

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  • 渐次进展
    2021-02-04 09:43

    I think this is what you're looking for:

    function getDefaultFontSize () {
// this will return the default* value assigned to the style: fontSize
defsize=(document.body.style.fontSize)
alert('The default font size of your browser is: "' + defsize + '"');
}

    *If body has a different fontSize decleration anywhere else in the code (perhaps in some css) the function will return that value. For example:

    <style>body{font-size:20px;}</style>
<script>function getDefaultFontSize () {
defsize=(document.body.style.fontSize)
} </script>

    The above will return a fontSize value of 20px.

    Fully tested and works for me (chrome 22.0.1229.94 m and firefox 13.01).

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  • 闹比i
    2021-02-04 09:44

    Using jQuery (assuming that you want the font size of a specific element):

    var originalFontSize = $('#your_element_id_here').css('font-size');

    If you're using Prototype as well as jQuery, you'll want to use the jQuery prefix instead of the dollar sign:

    var originalFontSize = jQuery('#your_element_id_here').css('font-size');

    This will return the value as a string like so: 16px.

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  • 滥情空心
    2021-02-04 09:50

    It can be done using this line of code:

    const fontSize = Number(window.getComputedStyle(document.body).getPropertyValue('font-size').match(/\d+/)[0])
    1. window.getComputedStyle(document.body) - to get all the styles for body
    2. getPropertyValue('font-size') - to get a string value of font-size, example: (16px)
    3. match(/\d+/)[0]) - to get only a number part, example: (16) - string
    4. Number(...) - to convert number part into a number, example: (16) - number
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