转换css单位

Question

我试图以所有有效"长度"和"百分比"单位取回一个样式属性,从该属性的原始值转换而来.

例如,如果我有一个div,style.width设置为20%,我想要一个具有该值的对象,以百分比(当然,20%),像素(无论实际像素宽度是多少),em,pt,前等

我意识到'百分比'不是'长度'值,并且并非所有接受长度值的属性都接受百分比,但也希望包括它.

当然,某些值将特定地依赖于元素,并且可能是它在DOM中的位置(例如,获取em值也将需要该元素的父计算字体大小).

我可以假设为该元素明确设置了样式 - 我知道如何检索元素的当前计算样式 - 我只是希望不重复其他人可能已经完成的工作.我也知道http://www.galasoft.ch/myjavascript/WebControls/css-length.html,但它依赖于style.pixelWidth或node.clientWidth,并在Chrome中失败(我认为它失败了Safari也是......以及其他人.)

我已经得到了颜色值(rgb,rgba,hex,name) - 这当然要简单得多.我正在使用数学上可变的值,因此实际上只需要'length'和'percent'值(如果在具有非长度,非百分比值的属性集上调用 - 如'font-size:larger' - 函数可能会失败,或抛出错误).

如果以程序方式编写,这样的事情将是理想的:

function getUnits(target, prop){
  var value = // get target's computed style property value
  // figure out what unit is being used natively, and it's values - for this e.g., 100px
  var units = {};
  units.pixel = 100;
  units.percent = 50;  // e.g., if the prop was height and the parent was 200px tall
  units.inch = 1.39;  // presumably units.pixel / 72 would work, but i'm not positive
  units.point = units.inch / 72;
  units.pica = units.point * 12;
  // etc...
  return units;
}

我并不是要求有人为我编写代码,但我希望有人之前已经这样做了,而且它可以在一些开源库,框架,博客文章,tut等等中使用.失败的是,如果有人聪明地想要如何简化流程,那也会很棒(上面链接的作者创建了一个临时div并计算了一个单独的值来确定其他单位的比例 - 一个方便的想法但是不是我完全卖掉的,绝对是一个需要补充逻辑来处理我希望接受的一切的东西.

提前感谢任何见解或建议.

Answer 1

编辑:更新以允许用户选择要返回的单个单元(例如,存在为%,以px返回) - 当性能足够大时性能的大幅提升 - 可能最终将其更改为仅接受单个单元进行转换,并摆脱循环.感谢无眼界的帮助./编辑

这就是我想出来的 - 经过初步测试后似乎有效.我从原始问题中提到的链接借用了临时div的想法,但这是关于从其他类中获取的所有内容.

如果有人有任何意见或改进,我会很高兴听到它.

   (function(){

    // pass to string.replace for camel to hyphen
    var hyphenate = function(a, b, c){
        return b + "-" + c.toLowerCase();
    }

    // get computed style property
    var getStyle = function(target, prop){
        if(prop in target.style){  // if it's explicitly assigned, just grab that
            if(!!(target.style[prop]) || target.style[prop] === 0){
                return target.style[prop];
            }
        }
        if(window.getComputedStyle){ // gecko and webkit
            prop = prop.replace(/([a-z])([A-Z])/, hyphenate);  // requires hyphenated, not camel
            return window.getComputedStyle(target, null).getPropertyValue(prop);
        }
        if(target.currentStyle){ // ie
            return target.currentStyle[prop];
        }
        return null;
    }

    // get object with units
    var getUnits = function(target, prop, returnUnit){

        var baseline = 100;  // any number serves 
        var item;  // generic iterator

        var map = {  // list of all units and their identifying string
            pixel : "px",
            percent : "%",
            inch : "in",
            cm : "cm",
            mm : "mm",
            point : "pt",
            pica : "pc",
            em : "em",
            ex : "ex"
        };

        var factors = {};  // holds ratios
        var units = {};  // holds calculated values

        var value = getStyle(target, prop);  // get the computed style value

        var numeric = value.match(/\d+/);  // get the numeric component
        if(numeric === null) {  // if match returns null, throw error...  use === so 0 values are accepted
            throw "Invalid property value returned";
        }
        numeric = numeric[0];  // get the string

        var unit = value.match(/\D+$/);  // get the existing unit
        unit = (unit == null) ? "px" : unit[0]; // if its not set, assume px - otherwise grab string

        var activeMap;  // a reference to the map key for the existing unit
        for(item in map){
            if(map[item] == unit){
                activeMap = item;
                break;
            }
        }
        if(!activeMap) { // if existing unit isn't in the map, throw an error
            throw "Unit not found in map";
        }

        var singleUnit = false;  // return object (all units) or string (one unit)?
        if(returnUnit && (typeof returnUnit == "string")) {  // if user wants only one unit returned, delete other maps
            for(item in map){
                if(map[item] == returnUnit){
                    singleUnit = item;
                    continue;
                }
                delete map[item];
            }
        }

        var temp = document.createElement("div");  // create temporary element
        temp.style.overflow = "hidden";  // in case baseline is set too low
        temp.style.visibility = "hidden";  // no need to show it

        target.parentNode.appendChild(temp);    // insert it into the parent for em and ex  

        for(item in map){  // set the style for each unit, then calculate it's relative value against the baseline
            temp.style.width = baseline + map[item];
            factors[item] = baseline / temp.offsetWidth;
        }

        for(item in map){  // use the ratios figured in the above loop to determine converted values
            units[item] = (numeric * (factors[item] * factors[activeMap])) + map[item];
        }

        target.parentNode.removeChild(temp);  // clean up

        if(singleUnit !== false){  // if they just want one unit back
            return units[singleUnit];
        }

        return units;  // returns the object with converted unit values...

    }

    // expose           
    window.getUnits = this.getUnits = getUnits;

})();

tyia

Answer 2

晚会了，我认为这不一定能完全回答问题，因为我没有包括百分比转换。然而，我确实认为这是一个好的开始，可以根据您的具体用途轻松修改。

JavaScript 函数

/**
 * Convert absolute CSS numerical values to pixels.
 *
 * @link https://developer.mozilla.org/en-US/docs/Learn/CSS/Building_blocks/Values_and_units#numbers_lengths_and_percentages
 *
 * @param {string} cssValue
 * @param {null|HTMLElement} target Used for relative units.
 * @return {*}
 */
window.convertCssUnit = function( cssValue, target ) {

    target = target || document.body;

    const supportedUnits = {

        // Absolute sizes
        'px': value => value,
        'cm': value => value * 38,
        'mm': value => value * 3.8,
        'q': value => value * 0.95,
        'in': value => value * 96,
        'pc': value => value * 16,
        'pt': value => value * 1.333333,

        // Relative sizes
        'rem': value => value * parseFloat( getComputedStyle( document.documentElement ).fontSize ),
        'em': value => value * parseFloat( getComputedStyle( target ).fontSize ),
        'vw': value => value / 100 * window.innerWidth,
        'vh': value => value / 100 * window.innerHeight,

        // Times
        'ms': value => value,
        's': value => value * 1000,

        // Angles
        'deg': value => value,
        'rad': value => value * ( 180 / Math.PI ),
        'grad': value => value * ( 180 / 200 ),
        'turn': value => value * 360

    };

    // Match positive and negative numbers including decimals with following unit
    const pattern = new RegExp( `^([\-\+]?(?:\\d+(?:\\.\\d+)?))(${ Object.keys( supportedUnits ).join( '|' ) })$`, 'i' );

    // If is a match, return example: [ "-2.75rem", "-2.75", "rem" ]
    const matches = String.prototype.toString.apply( cssValue ).trim().match( pattern );

    if ( matches ) {
        const value = Number( matches[ 1 ] );
        const unit = matches[ 2 ].toLocaleLowerCase();

        // Sanity check, make sure unit conversion function exists
        if ( unit in supportedUnits ) {
            return supportedUnits[ unit ]( value );
        }
    }

    return cssValue;

};

用法示例

// Convert rem value to pixels
const remExample = convertCssUnit( '2.5rem' );

// Convert time unit (seconds) to milliseconds
const speedExample = convertCssUnit( '2s' );

// Convert angle unit (grad) to degrees
const emExample = convertCssUnit( '200grad' );

// Convert vw value to pixels
const vwExample = convertCssUnit( '80vw' );

// Convert the css variable to pixels
const varExample = convertCssUnit( getComputedStyle( document.body ).getPropertyValue( '--container-width' ) );

// Convert `em` value relative to page element
const emExample = convertCssUnit( '2em', document.getElementById( '#my-element' ) );

当前支持的格式

前面带有加号 ( +) 或减号 ( ) 符号的任何格式-以及以下任何单位均有效：px, cm, mm, q, , in, pc, pt, , rem, em, vw, vh, s, ms, deg, rad,gradturn

例如：

10rem
10.2em
-0.34cm
+10.567s

您可以在此处查看完整的格式组合：https://jsfiddle.net/thelevicole/k7yt4naw/1/