解析 CSS 可能要复杂得多，需要记住的事情很少：
- 避免编写解析器 - 其他人可能已经编写了解析器（搜索）。
- 如果您不控制输入源或不使用输入样本彻底测试，您的解析器可能会失败。
- 在渐变的情况下，您可以有“角度”以及“角边”，如“右”。
- 存在未知数量的色标（最少 1 个）。
- 您绝不可能希望在正则表达式中包含完整的 CSS 颜色列表（例如
red、blue 等）。
- 您应该查看MDN 了解语法变化的详细信息，下面的示例代码仅支持标准语法。
- 正则表达式支持和错误因浏览器和版本而异 - 使用所有示例测试您的目标浏览器。
好的，这里有一个疯狂的例子，说明你如何“可以”使用正则表达式解析渐变 - 我并不是说你应该这样做。
在这里，我在代码中构建了我的正则表达式，以保持代码的某种程度的可读性和可维护性。
test_this_thing函数console.log(result);的最终输出如下：
输入：
background-image:linear-gradient(to right bottom, #FF0000 0%, #00FF00 20px, rgb(0, 0, 255) 100%);
输出：
{
original:"to right bottom, #FF0000 0%, #00FF00 20px, rgb(0, 0, 255) 100%",
line:"to right bottom",
sideCorner:"right bottom",
colorStopList:[
{
color:"#FF0000",
position:"0%"
},
{
color:"#00FF00",
position:"20px"
},
{
color:"rgb(0, 0, 255)",
position:"100%"
}
]
}
请注意，输出包含original 属性——这看起来像输入——但如果部分输入不匹配，input 和original 的值会有所不同；注意解析器中可能存在的错误。
这是一个来源：
/**
* Utility combine multiple regular expressions.
*
* @param {RegExp[]|string[]} regexpList List of regular expressions or strings.
* @param {string} flags Normal RegExp flags.
*/
var combineRegExp = function (regexpList, flags) {
var i,
source = '';
for (i = 0; i < regexpList.length; i++) {
if (typeof regexpList[i] === 'string') {
source += regexpList[i];
} else {
source += regexpList[i].source;
}
}
return new RegExp(source, flags);
};
/**
* Generate the required regular expressions once.
*
* Regular Expressions are easier to manage this way and can be well described.
*
* @result {object} Object containing regular expressions.
*/
var generateRegExp = function () {
// Note any variables with "Capture" in name include capturing bracket set(s).
var searchFlags = 'gi', // ignore case for angles, "rgb" etc
rAngle = /(?:[+-]?\d*\.?\d+)(?:deg|grad|rad|turn)/, // Angle +ive, -ive and angle types
rSideCornerCapture = /to\s+((?:(?:left|right)(?:\s+(?:top|bottom))?))/, // optional 2nd part
rComma = /\s*,\s*/, // Allow space around comma.
rColorHex = /\#(?:[a-f0-9]{6}|[a-f0-9]{3})/, // 3 or 6 character form
rDigits3 = /\(\s*(?:\d{1,3}\s*,\s*){2}\d{1,3}\s*\)/,// "(1, 2, 3)"
rDigits4 = /\(\s*(?:\d{1,3}\s*,\s*){2}\d{1,3}\s*,\s*\d*\.?\d+\)/,// "(1, 2, 3, 4)"
rValue = /(?:[+-]?\d*\.?\d+)(?:%|[a-z]+)?/,// ".9", "-5px", "100%".
rKeyword = /[_a-z-][_a-z0-9-]*/,// "red", "transparent", "border-collapse".
rColor = combineRegExp([
'(?:', rColorHex, '|', '(?:rgb|hsl)', rDigits3, '|', '(?:rgba|hsla)', rDigits4, '|', rKeyword, ')'
], ''),
rColorStop = combineRegExp([rColor, '(?:\\s+', rValue, '(?:\\s+', rValue, ')?)?'], ''),// Single Color Stop, optional %, optional length.
rColorStopList = combineRegExp(['(?:', rColorStop, rComma, ')*', rColorStop], ''),// List of color stops min 1.
rLineCapture = combineRegExp(['(?:(', rAngle, ')|', rSideCornerCapture, ')'], ''),// Angle or SideCorner
rGradientSearch = combineRegExp([
'(?:(', rLineCapture, ')', rComma, ')?(', rColorStopList, ')'
], searchFlags),// Capture 1:"line", 2:"angle" (optional), 3:"side corner" (optional) and 4:"stop list".
rColorStopSearch = combineRegExp([
'\\s*(', rColor, ')', '(?:\\s+', '(', rValue, '))?', '(?:', rComma, '\\s*)?'
], searchFlags);// Capture 1:"color" and 2:"position" (optional).
return {
gradientSearch: rGradientSearch,
colorStopSearch: rColorStopSearch
};
};
/**
* Actually parse the input gradient parameters string into an object for reusability.
*
*
* @note Really this only supports the standard syntax not historical versions, see MDN for details
* https://developer.mozilla.org/en-US/docs/Web/CSS/linear-gradient
*
* @param regExpLib
* @param {string} input Input string in the form "to right bottom, #FF0 0%, red 20px, rgb(0, 0, 255) 100%"
* @returns {object|undefined} Object containing break down of input string including array of stop points.
*/
var parseGradient = function (regExpLib, input) {
var result,
matchGradient,
matchColorStop,
stopResult;
// reset search position, because we reuse regex.
regExpLib.gradientSearch.lastIndex = 0;
matchGradient = regExpLib.gradientSearch.exec(input);
if (matchGradient !== null) {
result = {
original: matchGradient[0],
colorStopList: []
};
// Line (Angle or Side-Corner).
if (!!matchGradient[1]) {
result.line = matchGradient[1];
}
// Angle or undefined if side-corner.
if (!!matchGradient[2]) {
result.angle = matchGradient[2];
}
// Side-corner or undefined if angle.
if (!!matchGradient[3]) {
result.sideCorner = matchGradient[3];
}
// reset search position, because we reuse regex.
regExpLib.colorStopSearch.lastIndex = 0;
// Loop though all the color-stops.
matchColorStop = regExpLib.colorStopSearch.exec(matchGradient[4]);
while (matchColorStop !== null) {
stopResult = {
color: matchColorStop[1]
};
// Position (optional).
if (!!matchColorStop[2]) {
stopResult.position = matchColorStop[2];
}
result.colorStopList.push(stopResult);
// Continue searching from previous position.
matchColorStop = regExpLib.colorStopSearch.exec(matchGradient[4]);
}
}
// Can be undefined if match not found.
return result;
};
var test_this_one = function (regExpLib, input) {
var result,
rGradientEnclosedInBrackets = /.*gradient\s*\(((?:\([^\)]*\)|[^\)\(]*)*)\)/,// Captures inside brackets - max one additional inner set.
match = rGradientEnclosedInBrackets.exec(input);
if (match !== null) {
// Get the parameters for the gradient
result = parseGradient(regExpLib, match[1]);
if (result.original.trim() !== match[1].trim()) {
// Did not match the input exactly - possible parsing error.
result.parseWarning = true;
}
} else {
result = "Failed to find gradient";
}
return result;
};
var test_this_thing = function () {
var result = [],
regExpLib = generateRegExp(),
testSubjects = [
// Original question sample
'background-image:linear-gradient(to right bottom, #FF0000 0%, #00FF00 20px, rgb(0, 0, 255) 100%);',
// Sample to test RGBA values (1)
'background-image:linear-gradient(to right bottom, rgba(255, 0, 0, .1) 0%, rgba(0, 255, 0, 0.9) 20px);',
// Sample to test optional gradient line
'background-image:linear-gradient(#FF0000 0%, #00FF00 20px, rgb(0, 0, 255) 100%);',
// Angle, named colors
'background: linear-gradient(45deg, red, blue);',
// Gradient that starts at 60% of the gradient line
'background: linear-gradient(135deg, orange, orange 60%, cyan);',
// Gradient with multi-position color stops
'background: linear-gradient(to right, red 20%, orange 20% 40%, yellow 40% 60%, green 60% 80%, blue 80%);'
];
for (var i = 0; i < testSubjects.length; i++) {
result.push(test_this_one(regExpLib, testSubjects[i]));
}
console.log(result);
};
test_this_thing();